diff --git a/.gitignore b/.gitignore
index 897c80b1..e22101f2 100644
--- a/.gitignore
+++ b/.gitignore
@@ -6,3 +6,4 @@ phpunit.xml
 examples/public.key
 examples/private.key
 build
+*.orig
diff --git a/.travis.yml b/.travis.yml
index ae8f640c..b773c2aa 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -12,7 +12,6 @@ env:
   - DEPENDENCIES="--prefer-lowest --prefer-stable"
 
 php:
-  - 7.0
   - 7.1
   - 7.2
   - 7.3
@@ -31,3 +30,4 @@ after_script:
 branches:
   only:
     - master
+    - 8.0.0
diff --git a/CHANGELOG.md b/CHANGELOG.md
index e0721bc6..acfe9c1c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,27 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## [Unreleased]
 
+### Added
+- Flag, `requireCodeChallengeForPublicClients`, used to reject public clients that do not provide a code challenge for the Auth Code Grant; use AuthCodeGrant::disableRequireCodeCallengeForPublicClients() to turn off this requirement (PR #938)
+- Public clients can now use the Auth Code Grant (PR #938)
+- `isConfidential` getter added to `ClientEntity` to identify type of client (PR #938)
+- Function `validateClient()` added to validate clients which was previously performed by the `getClientEntity()` function (PR #938)
+- Add a new function to the AbstractGrant class called `getClientEntityOrFail()`. This is a wrapper around the `getClientEntity()` function that ensures we emit and throw an exception if the repo doesn't return a client entity. (PR #1010)
+
+### Changed
+- Replace `convertToJWT()` interface with a more generic `__toString()` to improve extensibility; AccessTokenEntityInterface now requires `setPrivateKey(CryptKey $privateKey)` so `__toString()` has everything it needs to work (PR #874)
+- The `invalidClient()` function accepts a PSR-7 compliant `$serverRequest` argument to avoid accessing the `$_SERVER` global variable and improve testing (PR #899)
+- `issueAccessToken()` in the Abstract Grant no longer sets access token client, user ID or scopes. These values should already have been set when calling `getNewToken()` (PR #919)
+- No longer need to enable PKCE with `enableCodeExchangeProof` flag. Any client sending a code challenge will initiate PKCE checks. (PR #938)
+- Function `getClientEntity()` no longer performs client validation (PR #938)
+- Password Grant now returns an invalid_grant error instead of invalid_credentials if a user cannot be validated (PR #967)
+- Use `DateTimeImmutable()` instead of `DateTime()`, `time()` instead of `(new DateTime())->getTimeStamp()`, and `DateTime::getTimeStamp()` instead of `DateTime::format('U')` (PR #963)
+
+### Removed
+- `enableCodeExchangeProof` flag (PR #938)
+- Support for PHP 7.0 (PR #1014)
+- Remove JTI claim from JWT header (PR #1031)
+
 ## [7.4.0] - released 2019-05-05
 
 ### Changed
diff --git a/README.md b/README.md
index ced17ed8..92a12f3e 100644
--- a/README.md
+++ b/README.md
@@ -31,12 +31,11 @@ This library was created by Alex Bilbie. Find him on Twitter at [@alexbilbie](ht
 
 The following versions of PHP are supported:
 
-* PHP 7.0
 * PHP 7.1
 * PHP 7.2
 * PHP 7.3
 
-The `openssl` extension is also required.
+The `openssl` and `json` extensions are also required.
 
 All HTTP messages passed to the server should be [PSR-7 compliant](https://www.php-fig.org/psr/psr-7/). This ensures interoperability with other packages and frameworks.
 
@@ -86,13 +85,9 @@ Bugs and feature request are tracked on [GitHub](https://github.com/thephpleague
 
 If you have any questions about OAuth _please_ open a ticket here; please **don't** email the address below.
 
-## Commercial Support
-
-If you would like help implementing this library into your existing platform, or would be interested in OAuth advice or training for you and your team please get in touch with [Glynde Labs](https://glyndelabs.com).
-
 ## Security
 
-If you discover any security related issues, please email `hello@alexbilbie.com` instead of using the issue tracker.
+If you discover any security related issues, please email `andrew@noexceptions.io` instead of using the issue tracker.
 
 ## License
 
@@ -100,7 +95,7 @@ This package is released under the MIT License. See the bundled [LICENSE](https:
 
 ## Credits
 
-This code is principally developed and maintained by [Andy Millington](https://twitter.com/Sephster) and [Simon Hamp](https://twitter.com/simonhamp).
+This code is principally developed and maintained by [Andy Millington](https://twitter.com/Sephster).
 
 Between 2012 and 2017 this library was developed and maintained by [Alex Bilbie](https://alexbilbie.com/).
 
diff --git a/composer.json b/composer.json
index cb54606c..7991a0cc 100644
--- a/composer.json
+++ b/composer.json
@@ -4,19 +4,19 @@
     "homepage": "https://oauth2.thephpleague.com/",
     "license": "MIT",
     "require": {
-        "php": ">=7.0.0",
+        "php": ">=7.1.0",
         "ext-openssl": "*",
-        "league/event": "^2.1",
-        "lcobucci/jwt": "^3.2.2",
+        "league/event": "^2.2",
+        "lcobucci/jwt": "^3.3.1",
         "psr/http-message": "^1.0.1",
-        "defuse/php-encryption": "^2.1"
+        "defuse/php-encryption": "^2.2.1",
+        "ext-json": "*"
     },
     "require-dev": {
-        "phpunit/phpunit": "^6.3 || ^7.0",
-        "zendframework/zend-diactoros": "^1.3.2",
-        "phpstan/phpstan": "^0.9.2",
-        "phpstan/phpstan-phpunit": "^0.9.4",
-        "phpstan/phpstan-strict-rules": "^0.9.0",
+        "phpunit/phpunit": "^7.5.13 || ^8.2.3",
+        "zendframework/zend-diactoros": "^2.1.2",
+        "phpstan/phpstan": "^0.11.8",
+        "phpstan/phpstan-phpunit": "^0.11.2",
         "roave/security-advisories": "dev-master"
     },
     "repositories": [
diff --git a/examples/composer.json b/examples/composer.json
index a3ef9b7a..ab0832fe 100644
--- a/examples/composer.json
+++ b/examples/composer.json
@@ -3,11 +3,11 @@
         "slim/slim": "^3.0.0"
     },
     "require-dev": {
-        "league/event": "^2.1",
-        "lcobucci/jwt": "^3.2",
+        "league/event": "^2.2",
+        "lcobucci/jwt": "^3.3",
         "psr/http-message": "^1.0",
         "defuse/php-encryption": "^2.2",
-        "zendframework/zend-diactoros": "^2.0.0"
+        "zendframework/zend-diactoros": "^2.1.0"
     },
     "autoload": {
         "psr-4": {
diff --git a/examples/composer.lock b/examples/composer.lock
index 6ba8ec13..d557b685 100644
--- a/examples/composer.lock
+++ b/examples/composer.lock
@@ -1,10 +1,10 @@
 {
     "_readme": [
         "This file locks the dependencies of your project to a known state",
-        "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#composer-lock-the-lock-file",
+        "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
         "This file is @generated automatically"
     ],
-    "content-hash": "97f2878428e37d1d8e5418cc85cbfa3d",
+    "content-hash": "a7f5c3fdcadb17399bbd97f15e1b11f1",
     "packages": [
         {
             "name": "container-interop/container-interop",
@@ -234,16 +234,16 @@
         },
         {
             "name": "slim/slim",
-            "version": "3.11.0",
+            "version": "3.12.1",
             "source": {
                 "type": "git",
                 "url": "https://github.com/slimphp/Slim.git",
-                "reference": "d378e70431e78ee92ee32ddde61ecc72edf5dc0a"
+                "reference": "eaee12ef8d0750db62b8c548016d82fb33addb6b"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/slimphp/Slim/zipball/d378e70431e78ee92ee32ddde61ecc72edf5dc0a",
-                "reference": "d378e70431e78ee92ee32ddde61ecc72edf5dc0a",
+                "url": "https://api.github.com/repos/slimphp/Slim/zipball/eaee12ef8d0750db62b8c548016d82fb33addb6b",
+                "reference": "eaee12ef8d0750db62b8c548016d82fb33addb6b",
                 "shasum": ""
             },
             "require": {
@@ -301,7 +301,7 @@
                 "micro",
                 "router"
             ],
-            "time": "2018-09-16T10:54:21+00:00"
+            "time": "2019-04-16T16:47:29+00:00"
         }
     ],
     "packages-dev": [
@@ -370,33 +370,30 @@
         },
         {
             "name": "lcobucci/jwt",
-            "version": "3.2.4",
+            "version": "3.3.1",
             "source": {
                 "type": "git",
                 "url": "https://github.com/lcobucci/jwt.git",
-                "reference": "c9704b751315d21735dc98d78d4f37bd73596da7"
+                "reference": "a11ec5f4b4d75d1fcd04e133dede4c317aac9e18"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/lcobucci/jwt/zipball/c9704b751315d21735dc98d78d4f37bd73596da7",
-                "reference": "c9704b751315d21735dc98d78d4f37bd73596da7",
+                "url": "https://api.github.com/repos/lcobucci/jwt/zipball/a11ec5f4b4d75d1fcd04e133dede4c317aac9e18",
+                "reference": "a11ec5f4b4d75d1fcd04e133dede4c317aac9e18",
                 "shasum": ""
             },
             "require": {
+                "ext-mbstring": "*",
                 "ext-openssl": "*",
-                "php": ">=5.5"
+                "php": "^5.6 || ^7.0"
             },
             "require-dev": {
-                "mdanter/ecc": "~0.3.1",
                 "mikey179/vfsstream": "~1.5",
                 "phpmd/phpmd": "~2.2",
                 "phpunit/php-invoker": "~1.1",
-                "phpunit/phpunit": "~4.5",
+                "phpunit/phpunit": "^5.7 || ^7.3",
                 "squizlabs/php_codesniffer": "~2.3"
             },
-            "suggest": {
-                "mdanter/ecc": "Required to use Elliptic Curves based algorithms."
-            },
             "type": "library",
             "extra": {
                 "branch-alias": {
@@ -424,20 +421,20 @@
                 "JWS",
                 "jwt"
             ],
-            "time": "2018-08-03T11:23:50+00:00"
+            "time": "2019-05-24T18:30:49+00:00"
         },
         {
             "name": "league/event",
-            "version": "2.1.2",
+            "version": "2.2.0",
             "source": {
                 "type": "git",
                 "url": "https://github.com/thephpleague/event.git",
-                "reference": "e4bfc88dbcb60c8d8a2939a71f9813e141bbe4cd"
+                "reference": "d2cc124cf9a3fab2bb4ff963307f60361ce4d119"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/thephpleague/event/zipball/e4bfc88dbcb60c8d8a2939a71f9813e141bbe4cd",
-                "reference": "e4bfc88dbcb60c8d8a2939a71f9813e141bbe4cd",
+                "url": "https://api.github.com/repos/thephpleague/event/zipball/d2cc124cf9a3fab2bb4ff963307f60361ce4d119",
+                "reference": "d2cc124cf9a3fab2bb4ff963307f60361ce4d119",
                 "shasum": ""
             },
             "require": {
@@ -445,7 +442,7 @@
             },
             "require-dev": {
                 "henrikbjorn/phpspec-code-coverage": "~1.0.1",
-                "phpspec/phpspec": "~2.0.0"
+                "phpspec/phpspec": "^2.2"
             },
             "type": "library",
             "extra": {
@@ -474,7 +471,7 @@
                 "event",
                 "listener"
             ],
-            "time": "2015-05-21T12:24:47+00:00"
+            "time": "2018-11-26T11:52:41+00:00"
         },
         {
             "name": "paragonie/random_compat",
@@ -523,16 +520,16 @@
         },
         {
             "name": "psr/http-factory",
-            "version": "1.0.0",
+            "version": "1.0.1",
             "source": {
                 "type": "git",
                 "url": "https://github.com/php-fig/http-factory.git",
-                "reference": "378bfe27931ecc54ff824a20d6f6bfc303bbd04c"
+                "reference": "12ac7fcd07e5b077433f5f2bee95b3a771bf61be"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/php-fig/http-factory/zipball/378bfe27931ecc54ff824a20d6f6bfc303bbd04c",
-                "reference": "378bfe27931ecc54ff824a20d6f6bfc303bbd04c",
+                "url": "https://api.github.com/repos/php-fig/http-factory/zipball/12ac7fcd07e5b077433f5f2bee95b3a771bf61be",
+                "reference": "12ac7fcd07e5b077433f5f2bee95b3a771bf61be",
                 "shasum": ""
             },
             "require": {
@@ -571,20 +568,20 @@
                 "request",
                 "response"
             ],
-            "time": "2018-07-30T21:54:04+00:00"
+            "time": "2019-04-30T12:38:16+00:00"
         },
         {
             "name": "zendframework/zend-diactoros",
-            "version": "2.0.0",
+            "version": "2.1.3",
             "source": {
                 "type": "git",
                 "url": "https://github.com/zendframework/zend-diactoros.git",
-                "reference": "0bae78192e634774b5584f0210c1232da82cb1ff"
+                "reference": "279723778c40164bcf984a2df12ff2c6ec5e61c1"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/zendframework/zend-diactoros/zipball/0bae78192e634774b5584f0210c1232da82cb1ff",
-                "reference": "0bae78192e634774b5584f0210c1232da82cb1ff",
+                "url": "https://api.github.com/repos/zendframework/zend-diactoros/zipball/279723778c40164bcf984a2df12ff2c6ec5e61c1",
+                "reference": "279723778c40164bcf984a2df12ff2c6ec5e61c1",
                 "shasum": ""
             },
             "require": {
@@ -607,8 +604,8 @@
             "type": "library",
             "extra": {
                 "branch-alias": {
-                    "dev-master": "2.0.x-dev",
-                    "dev-develop": "2.1.x-dev",
+                    "dev-master": "2.1.x-dev",
+                    "dev-develop": "2.2.x-dev",
                     "dev-release-1.8": "1.8.x-dev"
                 }
             },
@@ -637,7 +634,7 @@
                 "psr",
                 "psr-7"
             ],
-            "time": "2018-09-27T19:49:04+00:00"
+            "time": "2019-07-10T16:13:25+00:00"
         }
     ],
     "aliases": [],
diff --git a/examples/src/Repositories/ClientRepository.php b/examples/src/Repositories/ClientRepository.php
index eaa4e5c2..47db508c 100644
--- a/examples/src/Repositories/ClientRepository.php
+++ b/examples/src/Repositories/ClientRepository.php
@@ -14,16 +14,33 @@ use OAuth2ServerExamples\Entities\ClientEntity;
 
 class ClientRepository implements ClientRepositoryInterface
 {
+    const CLIENT_NAME = 'My Awesome App';
+    const REDIRECT_URI = 'http://foo/bar';
+
     /**
      * {@inheritdoc}
      */
-    public function getClientEntity($clientIdentifier, $grantType = null, $clientSecret = null, $mustValidateSecret = true)
+    public function getClientEntity($clientIdentifier)
+    {
+        $client = new ClientEntity();
+
+        $client->setIdentifier($clientIdentifier);
+        $client->setName(self::CLIENT_NAME);
+        $client->setRedirectUri(self::REDIRECT_URI);
+
+        return $client;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function validateClient($clientIdentifier, $clientSecret, $grantType)
     {
         $clients = [
             'myawesomeapp' => [
                 'secret'          => password_hash('abc123', PASSWORD_BCRYPT),
-                'name'            => 'My Awesome App',
-                'redirect_uri'    => 'http://foo/bar',
+                'name'            => self::CLIENT_NAME,
+                'redirect_uri'    => self::REDIRECT_URI,
                 'is_confidential' => true,
             ],
         ];
@@ -34,18 +51,10 @@ class ClientRepository implements ClientRepositoryInterface
         }
 
         if (
-            $mustValidateSecret === true
-            && $clients[$clientIdentifier]['is_confidential'] === true
+            $clients[$clientIdentifier]['is_confidential'] === true
             && password_verify($clientSecret, $clients[$clientIdentifier]['secret']) === false
         ) {
             return;
         }
-
-        $client = new ClientEntity();
-        $client->setIdentifier($clientIdentifier);
-        $client->setName($clients[$clientIdentifier]['name']);
-        $client->setRedirectUri($clients[$clientIdentifier]['redirect_uri']);
-
-        return $client;
     }
 }
diff --git a/phpstan.neon b/phpstan.neon
index 5cd9d80d..ba1fb491 100644
--- a/phpstan.neon
+++ b/phpstan.neon
@@ -1,8 +1,6 @@
 includes:
 	- vendor/phpstan/phpstan-phpunit/extension.neon
 	- vendor/phpstan/phpstan-phpunit/rules.neon
-	- vendor/phpstan/phpstan-phpunit/strictRules.neon
-	- vendor/phpstan/phpstan-strict-rules/rules.neon
 services:
 	-
 		class: LeagueTests\PHPStan\AbstractGrantExtension
diff --git a/src/AuthorizationServer.php b/src/AuthorizationServer.php
index bde97d6e..8b0b2815 100644
--- a/src/AuthorizationServer.php
+++ b/src/AuthorizationServer.php
@@ -125,7 +125,7 @@ class AuthorizationServer implements EmitterAwareInterface
      */
     public function enableGrantType(GrantTypeInterface $grantType, DateInterval $accessTokenTTL = null)
     {
-        if ($accessTokenTTL instanceof DateInterval === false) {
+        if ($accessTokenTTL === null) {
             $accessTokenTTL = new DateInterval('PT1H');
         }
 
diff --git a/src/AuthorizationValidators/BearerTokenValidator.php b/src/AuthorizationValidators/BearerTokenValidator.php
index b2035ccc..7218f413 100644
--- a/src/AuthorizationValidators/BearerTokenValidator.php
+++ b/src/AuthorizationValidators/BearerTokenValidator.php
@@ -63,7 +63,7 @@ class BearerTokenValidator implements AuthorizationValidatorInterface
         }
 
         $header = $request->getHeader('authorization');
-        $jwt = trim(preg_replace('/^(?:\s+)?Bearer\s/', '', $header[0]));
+        $jwt = trim((string) preg_replace('/^(?:\s+)?Bearer\s/', '', $header[0]));
 
         try {
             // Attempt to parse and validate the JWT
diff --git a/src/CodeChallengeVerifiers/CodeChallengeVerifierInterface.php b/src/CodeChallengeVerifiers/CodeChallengeVerifierInterface.php
new file mode 100644
index 00000000..3d7ad59c
--- /dev/null
+++ b/src/CodeChallengeVerifiers/CodeChallengeVerifierInterface.php
@@ -0,0 +1,30 @@
+<?php
+/**
+ * @author      Lukáš Unger <lookymsc@gmail.com>
+ * @copyright   Copyright (c) Lukáš Unger
+ * @license     http://mit-license.org/
+ *
+ * @link        https://github.com/thephpleague/oauth2-server
+ */
+
+namespace League\OAuth2\Server\CodeChallengeVerifiers;
+
+interface CodeChallengeVerifierInterface
+{
+    /**
+     * Return code challenge method.
+     *
+     * @return string
+     */
+    public function getMethod();
+
+    /**
+     * Verify the code challenge.
+     *
+     * @param string $codeVerifier
+     * @param string $codeChallenge
+     *
+     * @return bool
+     */
+    public function verifyCodeChallenge($codeVerifier, $codeChallenge);
+}
diff --git a/src/CodeChallengeVerifiers/PlainVerifier.php b/src/CodeChallengeVerifiers/PlainVerifier.php
new file mode 100644
index 00000000..71749c97
--- /dev/null
+++ b/src/CodeChallengeVerifiers/PlainVerifier.php
@@ -0,0 +1,36 @@
+<?php
+/**
+ * @author      Lukáš Unger <lookymsc@gmail.com>
+ * @copyright   Copyright (c) Lukáš Unger
+ * @license     http://mit-license.org/
+ *
+ * @link        https://github.com/thephpleague/oauth2-server
+ */
+
+namespace League\OAuth2\Server\CodeChallengeVerifiers;
+
+class PlainVerifier implements CodeChallengeVerifierInterface
+{
+    /**
+     * Return code challenge method.
+     *
+     * @return string
+     */
+    public function getMethod()
+    {
+        return 'plain';
+    }
+
+    /**
+     * Verify the code challenge.
+     *
+     * @param string $codeVerifier
+     * @param string $codeChallenge
+     *
+     * @return bool
+     */
+    public function verifyCodeChallenge($codeVerifier, $codeChallenge)
+    {
+        return hash_equals($codeVerifier, $codeChallenge);
+    }
+}
diff --git a/src/CodeChallengeVerifiers/S256Verifier.php b/src/CodeChallengeVerifiers/S256Verifier.php
new file mode 100644
index 00000000..3b37af3a
--- /dev/null
+++ b/src/CodeChallengeVerifiers/S256Verifier.php
@@ -0,0 +1,39 @@
+<?php
+/**
+ * @author      Lukáš Unger <lookymsc@gmail.com>
+ * @copyright   Copyright (c) Lukáš Unger
+ * @license     http://mit-license.org/
+ *
+ * @link        https://github.com/thephpleague/oauth2-server
+ */
+
+namespace League\OAuth2\Server\CodeChallengeVerifiers;
+
+class S256Verifier implements CodeChallengeVerifierInterface
+{
+    /**
+     * Return code challenge method.
+     *
+     * @return string
+     */
+    public function getMethod()
+    {
+        return 'S256';
+    }
+
+    /**
+     * Verify the code challenge.
+     *
+     * @param string $codeVerifier
+     * @param string $codeChallenge
+     *
+     * @return bool
+     */
+    public function verifyCodeChallenge($codeVerifier, $codeChallenge)
+    {
+        return hash_equals(
+            strtr(rtrim(base64_encode(hash('sha256', $codeVerifier, true)), '='), '+/', '-_'),
+            $codeChallenge
+        );
+    }
+}
diff --git a/src/CryptTrait.php b/src/CryptTrait.php
index 1196e9dc..5709940d 100644
--- a/src/CryptTrait.php
+++ b/src/CryptTrait.php
@@ -19,7 +19,7 @@ use LogicException;
 trait CryptTrait
 {
     /**
-     * @var string|Key
+     * @var string|Key|null
      */
     protected $encryptionKey;
 
@@ -39,9 +39,13 @@ trait CryptTrait
                 return Crypto::encrypt($unencryptedData, $this->encryptionKey);
             }
 
-            return Crypto::encryptWithPassword($unencryptedData, $this->encryptionKey);
+            if (is_string($this->encryptionKey)) {
+                return Crypto::encryptWithPassword($unencryptedData, $this->encryptionKey);
+            }
+
+            throw new LogicException('Encryption key not set when attempting to encrypt');
         } catch (Exception $e) {
-            throw new LogicException($e->getMessage(), null, $e);
+            throw new LogicException($e->getMessage(), 0, $e);
         }
     }
 
@@ -61,9 +65,13 @@ trait CryptTrait
                 return Crypto::decrypt($encryptedData, $this->encryptionKey);
             }
 
-            return Crypto::decryptWithPassword($encryptedData, $this->encryptionKey);
+            if (is_string($this->encryptionKey)) {
+                return Crypto::decryptWithPassword($encryptedData, $this->encryptionKey);
+            }
+
+            throw new LogicException('Encryption key not set when attempting to decrypt');
         } catch (Exception $e) {
-            throw new LogicException($e->getMessage(), null, $e);
+            throw new LogicException($e->getMessage(), 0, $e);
         }
     }
 
diff --git a/src/Entities/AccessTokenEntityInterface.php b/src/Entities/AccessTokenEntityInterface.php
index 4da7600e..fd459914 100644
--- a/src/Entities/AccessTokenEntityInterface.php
+++ b/src/Entities/AccessTokenEntityInterface.php
@@ -9,17 +9,17 @@
 
 namespace League\OAuth2\Server\Entities;
 
-use Lcobucci\JWT\Token;
 use League\OAuth2\Server\CryptKey;
 
 interface AccessTokenEntityInterface extends TokenInterface
 {
     /**
-     * Generate a JWT from the access token
-     *
-     * @param CryptKey $privateKey
-     *
-     * @return Token
+     * Set a private key used to encrypt the access token.
      */
-    public function convertToJWT(CryptKey $privateKey);
+    public function setPrivateKey(CryptKey $privateKey);
+
+    /**
+     * Generate a string representation of the access token.
+     */
+    public function __toString();
 }
diff --git a/src/Entities/ClientEntityInterface.php b/src/Entities/ClientEntityInterface.php
index 80cc70c8..971c6124 100644
--- a/src/Entities/ClientEntityInterface.php
+++ b/src/Entities/ClientEntityInterface.php
@@ -33,4 +33,11 @@ interface ClientEntityInterface
      * @return string|string[]
      */
     public function getRedirectUri();
+
+    /**
+     * Returns true if the client is confidential.
+     *
+     * @return bool
+     */
+    public function isConfidential();
 }
diff --git a/src/Entities/RefreshTokenEntityInterface.php b/src/Entities/RefreshTokenEntityInterface.php
index c2898ae5..551ad052 100644
--- a/src/Entities/RefreshTokenEntityInterface.php
+++ b/src/Entities/RefreshTokenEntityInterface.php
@@ -9,7 +9,7 @@
 
 namespace League\OAuth2\Server\Entities;
 
-use DateTime;
+use DateTimeImmutable;
 
 interface RefreshTokenEntityInterface
 {
@@ -30,16 +30,16 @@ interface RefreshTokenEntityInterface
     /**
      * Get the token's expiry date time.
      *
-     * @return DateTime
+     * @return DateTimeImmutable
      */
     public function getExpiryDateTime();
 
     /**
      * Set the date time when the token expires.
      *
-     * @param DateTime $dateTime
+     * @param DateTimeImmutable $dateTime
      */
-    public function setExpiryDateTime(DateTime $dateTime);
+    public function setExpiryDateTime(DateTimeImmutable $dateTime);
 
     /**
      * Set the access token that the refresh token was associated with.
diff --git a/src/Entities/TokenInterface.php b/src/Entities/TokenInterface.php
index d2ca77d3..7b063e13 100644
--- a/src/Entities/TokenInterface.php
+++ b/src/Entities/TokenInterface.php
@@ -9,7 +9,7 @@
 
 namespace League\OAuth2\Server\Entities;
 
-use DateTime;
+use DateTimeImmutable;
 
 interface TokenInterface
 {
@@ -30,16 +30,16 @@ interface TokenInterface
     /**
      * Get the token's expiry date time.
      *
-     * @return DateTime
+     * @return DateTimeImmutable
      */
     public function getExpiryDateTime();
 
     /**
      * Set the date time when the token expires.
      *
-     * @param DateTime $dateTime
+     * @param DateTimeImmutable $dateTime
      */
-    public function setExpiryDateTime(DateTime $dateTime);
+    public function setExpiryDateTime(DateTimeImmutable $dateTime);
 
     /**
      * Set the identifier of the user associated with the token.
diff --git a/src/Entities/Traits/AccessTokenTrait.php b/src/Entities/Traits/AccessTokenTrait.php
index 5fa4a9be..44276de1 100644
--- a/src/Entities/Traits/AccessTokenTrait.php
+++ b/src/Entities/Traits/AccessTokenTrait.php
@@ -9,7 +9,7 @@
 
 namespace League\OAuth2\Server\Entities\Traits;
 
-use DateTime;
+use DateTimeImmutable;
 use Lcobucci\JWT\Builder;
 use Lcobucci\JWT\Signer\Key;
 use Lcobucci\JWT\Signer\Rsa\Sha256;
@@ -20,6 +20,19 @@ use League\OAuth2\Server\Entities\ScopeEntityInterface;
 
 trait AccessTokenTrait
 {
+    /**
+     * @var CryptKey
+     */
+    private $privateKey;
+
+    /**
+     * Set the private key used to encrypt this access token.
+     */
+    public function setPrivateKey(CryptKey $privateKey)
+    {
+        $this->privateKey = $privateKey;
+    }
+
     /**
      * Generate a JWT from the access token
      *
@@ -27,27 +40,35 @@ trait AccessTokenTrait
      *
      * @return Token
      */
-    public function convertToJWT(CryptKey $privateKey)
+    private function convertToJWT(CryptKey $privateKey)
     {
         return (new Builder())
             ->setAudience($this->getClient()->getIdentifier())
-            ->setId($this->getIdentifier(), true)
+            ->setId($this->getIdentifier())
             ->setIssuedAt(time())
             ->setNotBefore(time())
             ->setExpiration($this->getExpiryDateTime()->getTimestamp())
-            ->setSubject($this->getUserIdentifier())
+            ->setSubject((string) $this->getUserIdentifier())
             ->set('scopes', $this->getScopes())
             ->sign(new Sha256(), new Key($privateKey->getKeyPath(), $privateKey->getPassPhrase()))
             ->getToken();
     }
 
+    /**
+     * Generate a string representation from the access token
+     */
+    public function __toString()
+    {
+        return (string) $this->convertToJWT($this->privateKey);
+    }
+
     /**
      * @return ClientEntityInterface
      */
     abstract public function getClient();
 
     /**
-     * @return DateTime
+     * @return DateTimeImmutable
      */
     abstract public function getExpiryDateTime();
 
diff --git a/src/Entities/Traits/ClientTrait.php b/src/Entities/Traits/ClientTrait.php
index fec76a6f..a0078d8d 100644
--- a/src/Entities/Traits/ClientTrait.php
+++ b/src/Entities/Traits/ClientTrait.php
@@ -21,6 +21,11 @@ trait ClientTrait
      */
     protected $redirectUri;
 
+    /**
+     * @var bool
+     */
+    protected $isConfidential = false;
+
     /**
      * Get the client's name.
      *
@@ -43,4 +48,14 @@ trait ClientTrait
     {
         return $this->redirectUri;
     }
+
+    /**
+     * Returns true if the client is confidential.
+     *
+     * @return bool
+     */
+    public function isConfidential()
+    {
+        return $this->isConfidential;
+    }
 }
diff --git a/src/Entities/Traits/RefreshTokenTrait.php b/src/Entities/Traits/RefreshTokenTrait.php
index 0734daf1..f0f15444 100644
--- a/src/Entities/Traits/RefreshTokenTrait.php
+++ b/src/Entities/Traits/RefreshTokenTrait.php
@@ -9,7 +9,7 @@
 
 namespace League\OAuth2\Server\Entities\Traits;
 
-use DateTime;
+use DateTimeImmutable;
 use League\OAuth2\Server\Entities\AccessTokenEntityInterface;
 
 trait RefreshTokenTrait
@@ -20,7 +20,7 @@ trait RefreshTokenTrait
     protected $accessToken;
 
     /**
-     * @var DateTime
+     * @var DateTimeImmutable
      */
     protected $expiryDateTime;
 
@@ -43,7 +43,7 @@ trait RefreshTokenTrait
     /**
      * Get the token's expiry date time.
      *
-     * @return DateTime
+     * @return DateTimeImmutable
      */
     public function getExpiryDateTime()
     {
@@ -53,9 +53,9 @@ trait RefreshTokenTrait
     /**
      * Set the date time when the token expires.
      *
-     * @param DateTime $dateTime
+     * @param DateTimeImmutable $dateTime
      */
-    public function setExpiryDateTime(DateTime $dateTime)
+    public function setExpiryDateTime(DateTimeImmutable $dateTime)
     {
         $this->expiryDateTime = $dateTime;
     }
diff --git a/src/Entities/Traits/TokenEntityTrait.php b/src/Entities/Traits/TokenEntityTrait.php
index 34159149..5275c462 100644
--- a/src/Entities/Traits/TokenEntityTrait.php
+++ b/src/Entities/Traits/TokenEntityTrait.php
@@ -9,7 +9,7 @@
 
 namespace League\OAuth2\Server\Entities\Traits;
 
-use DateTime;
+use DateTimeImmutable;
 use League\OAuth2\Server\Entities\ClientEntityInterface;
 use League\OAuth2\Server\Entities\ScopeEntityInterface;
 
@@ -21,7 +21,7 @@ trait TokenEntityTrait
     protected $scopes = [];
 
     /**
-     * @var DateTime
+     * @var DateTimeImmutable
      */
     protected $expiryDateTime;
 
@@ -58,7 +58,7 @@ trait TokenEntityTrait
     /**
      * Get the token's expiry date time.
      *
-     * @return DateTime
+     * @return DateTimeImmutable
      */
     public function getExpiryDateTime()
     {
@@ -68,9 +68,9 @@ trait TokenEntityTrait
     /**
      * Set the date time when the token expires.
      *
-     * @param DateTime $dateTime
+     * @param DateTimeImmutable $dateTime
      */
-    public function setExpiryDateTime(DateTime $dateTime)
+    public function setExpiryDateTime(DateTimeImmutable $dateTime)
     {
         $this->expiryDateTime = $dateTime;
     }
diff --git a/src/Exception/OAuthServerException.php b/src/Exception/OAuthServerException.php
index bb448767..8e628baa 100644
--- a/src/Exception/OAuthServerException.php
+++ b/src/Exception/OAuthServerException.php
@@ -11,6 +11,7 @@ namespace League\OAuth2\Server\Exception;
 
 use Exception;
 use Psr\Http\Message\ResponseInterface;
+use Psr\Http\Message\ServerRequestInterface;
 use Throwable;
 
 class OAuthServerException extends Exception
@@ -40,6 +41,11 @@ class OAuthServerException extends Exception
      */
     private $payload;
 
+    /**
+     * @var ServerRequestInterface
+     */
+    private $serverRequest;
+
     /**
      * Throw a new exception.
      *
@@ -95,6 +101,16 @@ class OAuthServerException extends Exception
         $this->payload = $payload;
     }
 
+    /**
+     * Set the server request that is responsible for generating the exception
+     *
+     * @param ServerRequestInterface $serverRequest
+     */
+    public function setServerRequest(ServerRequestInterface $serverRequest)
+    {
+        $this->serverRequest = $serverRequest;
+    }
+
     /**
      * Unsupported grant type error.
      *
@@ -129,13 +145,17 @@ class OAuthServerException extends Exception
     /**
      * Invalid client error.
      *
+     * @param ServerRequestInterface $serverRequest
+     *
      * @return static
      */
-    public static function invalidClient()
+    public static function invalidClient(ServerRequestInterface $serverRequest)
     {
-        $errorMessage = 'Client authentication failed';
+        $exception = new static('Client authentication failed', 4, 'invalid_client', 401);
 
-        return new static($errorMessage, 4, 'invalid_client', 401);
+        $exception->setServerRequest($serverRequest);
+
+        return $exception;
     }
 
     /**
@@ -288,7 +308,9 @@ class OAuthServerException extends Exception
             $response = $response->withHeader($header, $content);
         }
 
-        $response->getBody()->write(json_encode($payload, $jsonOptions));
+        $responseBody = json_encode($payload, $jsonOptions) ?: 'JSON encoding of payload failed';
+
+        $response->getBody()->write($responseBody);
 
         return $response->withStatus($this->getHttpStatusCode());
     }
@@ -313,8 +335,8 @@ class OAuthServerException extends Exception
         // include the "WWW-Authenticate" response header field
         // matching the authentication scheme used by the client.
         // @codeCoverageIgnoreStart
-        if ($this->errorType === 'invalid_client' && array_key_exists('HTTP_AUTHORIZATION', $_SERVER) !== false) {
-            $authScheme = strpos($_SERVER['HTTP_AUTHORIZATION'], 'Bearer') === 0 ? 'Bearer' : 'Basic';
+        if ($this->errorType === 'invalid_client' && $this->serverRequest->hasHeader('Authorization') === true) {
+            $authScheme = strpos($this->serverRequest->getHeader('Authorization')[0], 'Bearer') === 0 ? 'Bearer' : 'Basic';
 
             $headers['WWW-Authenticate'] = $authScheme . ' realm="OAuth"';
         }
diff --git a/src/Grant/AbstractGrant.php b/src/Grant/AbstractGrant.php
index 6d7ff18d..0ac9e395 100644
--- a/src/Grant/AbstractGrant.php
+++ b/src/Grant/AbstractGrant.php
@@ -11,7 +11,7 @@
 namespace League\OAuth2\Server\Grant;
 
 use DateInterval;
-use DateTime;
+use DateTimeImmutable;
 use Error;
 use Exception;
 use League\Event\EmitterAwareTrait;
@@ -177,28 +177,17 @@ abstract class AbstractGrant implements GrantTypeInterface
      */
     protected function validateClient(ServerRequestInterface $request)
     {
-        list($basicAuthUser, $basicAuthPassword) = $this->getBasicAuthCredentials($request);
+        list($clientId, $clientSecret) = $this->getClientCredentials($request);
 
-        $clientId = $this->getRequestParameter('client_id', $request, $basicAuthUser);
-        if ($clientId === null) {
-            throw OAuthServerException::invalidRequest('client_id');
-        }
-
-        // If the client is confidential require the client secret
-        $clientSecret = $this->getRequestParameter('client_secret', $request, $basicAuthPassword);
-
-        $client = $this->clientRepository->getClientEntity(
-            $clientId,
-            $this->getIdentifier(),
-            $clientSecret,
-            true
-        );
-
-        if ($client instanceof ClientEntityInterface === false) {
+        if ($this->clientRepository->validateClient($clientId, $clientSecret, $this->getIdentifier()) === false) {
             $this->getEmitter()->emit(new RequestEvent(RequestEvent::CLIENT_AUTHENTICATION_FAILED, $request));
-            throw OAuthServerException::invalidClient();
+
+            throw OAuthServerException::invalidClient($request);
         }
 
+        $client = $this->getClientEntityOrFail($clientId, $request);
+
+        // If a redirect URI is provided ensure it matches what is pre-registered
         $redirectUri = $this->getRequestParameter('redirect_uri', $request, null);
 
         if ($redirectUri !== null) {
@@ -208,6 +197,56 @@ abstract class AbstractGrant implements GrantTypeInterface
         return $client;
     }
 
+    /**
+     * Wrapper around ClientRepository::getClientEntity() that ensures we emit
+     * an event and throw an exception if the repo doesn't return a client
+     * entity.
+     *
+     * This is a bit of defensive coding because the interface contract
+     * doesn't actually enforce non-null returns/exception-on-no-client so
+     * getClientEntity might return null. By contrast, this method will
+     * always either return a ClientEntityInterface or throw.
+     *
+     * @param string                 $clientId
+     * @param ServerRequestInterface $request
+     *
+     * @return ClientEntityInterface
+     */
+    protected function getClientEntityOrFail($clientId, ServerRequestInterface $request)
+    {
+        $client = $this->clientRepository->getClientEntity($clientId);
+
+        if ($client instanceof ClientEntityInterface === false) {
+            $this->getEmitter()->emit(new RequestEvent(RequestEvent::CLIENT_AUTHENTICATION_FAILED, $request));
+            throw OAuthServerException::invalidClient($request);
+        }
+
+        return $client;
+    }
+
+    /**
+     * Gets the client credentials from the request from the request body or
+     * the Http Basic Authorization header
+     *
+     * @param ServerRequestInterface $request
+     *
+     * @return array
+     */
+    protected function getClientCredentials(ServerRequestInterface $request)
+    {
+        list($basicAuthUser, $basicAuthPassword) = $this->getBasicAuthCredentials($request);
+
+        $clientId = $this->getRequestParameter('client_id', $request, $basicAuthUser);
+
+        if (is_null($clientId)) {
+            throw OAuthServerException::invalidRequest('client_id');
+        }
+
+        $clientSecret = $this->getRequestParameter('client_secret', $request, $basicAuthPassword);
+
+        return [$clientId, $clientSecret];
+    }
+
     /**
      * Validate redirectUri from the request.
      * If a redirect URI is provided ensure it matches what is pre-registered
@@ -227,12 +266,12 @@ abstract class AbstractGrant implements GrantTypeInterface
             && (strcmp($client->getRedirectUri(), $redirectUri) !== 0)
         ) {
             $this->getEmitter()->emit(new RequestEvent(RequestEvent::CLIENT_AUTHENTICATION_FAILED, $request));
-            throw OAuthServerException::invalidClient();
+            throw OAuthServerException::invalidClient($request);
         } elseif (\is_array($client->getRedirectUri())
             && \in_array($redirectUri, $client->getRedirectUri(), true) === false
         ) {
             $this->getEmitter()->emit(new RequestEvent(RequestEvent::CLIENT_AUTHENTICATION_FAILED, $request));
-            throw OAuthServerException::invalidClient();
+            throw OAuthServerException::invalidClient($request);
         }
     }
 
@@ -394,13 +433,8 @@ abstract class AbstractGrant implements GrantTypeInterface
         $maxGenerationAttempts = self::MAX_RANDOM_TOKEN_GENERATION_ATTEMPTS;
 
         $accessToken = $this->accessTokenRepository->getNewToken($client, $scopes, $userIdentifier);
-        $accessToken->setClient($client);
-        $accessToken->setUserIdentifier($userIdentifier);
-        $accessToken->setExpiryDateTime((new DateTime())->add($accessTokenTTL));
-
-        foreach ($scopes as $scope) {
-            $accessToken->addScope($scope);
-        }
+        $accessToken->setExpiryDateTime((new DateTimeImmutable())->add($accessTokenTTL));
+        $accessToken->setPrivateKey($this->privateKey);
 
         while ($maxGenerationAttempts-- > 0) {
             $accessToken->setIdentifier($this->generateUniqueIdentifier());
@@ -440,7 +474,7 @@ abstract class AbstractGrant implements GrantTypeInterface
         $maxGenerationAttempts = self::MAX_RANDOM_TOKEN_GENERATION_ATTEMPTS;
 
         $authCode = $this->authCodeRepository->getNewAuthCode();
-        $authCode->setExpiryDateTime((new DateTime())->add($authCodeTTL));
+        $authCode->setExpiryDateTime((new DateTimeImmutable())->add($authCodeTTL));
         $authCode->setClient($client);
         $authCode->setUserIdentifier($userIdentifier);
 
@@ -482,7 +516,7 @@ abstract class AbstractGrant implements GrantTypeInterface
             return null;
         }
 
-        $refreshToken->setExpiryDateTime((new DateTime())->add($this->refreshTokenTTL));
+        $refreshToken->setExpiryDateTime((new DateTimeImmutable())->add($this->refreshTokenTTL));
         $refreshToken->setAccessToken($accessToken);
 
         $maxGenerationAttempts = self::MAX_RANDOM_TOKEN_GENERATION_ATTEMPTS;
diff --git a/src/Grant/AuthCodeGrant.php b/src/Grant/AuthCodeGrant.php
index 350fdde5..f85a0898 100644
--- a/src/Grant/AuthCodeGrant.php
+++ b/src/Grant/AuthCodeGrant.php
@@ -10,8 +10,11 @@
 namespace League\OAuth2\Server\Grant;
 
 use DateInterval;
-use DateTime;
+use DateTimeImmutable;
 use Exception;
+use League\OAuth2\Server\CodeChallengeVerifiers\CodeChallengeVerifierInterface;
+use League\OAuth2\Server\CodeChallengeVerifiers\PlainVerifier;
+use League\OAuth2\Server\CodeChallengeVerifiers\S256Verifier;
 use League\OAuth2\Server\Entities\ClientEntityInterface;
 use League\OAuth2\Server\Entities\UserEntityInterface;
 use League\OAuth2\Server\Exception\OAuthServerException;
@@ -35,7 +38,12 @@ class AuthCodeGrant extends AbstractAuthorizeGrant
     /**
      * @var bool
      */
-    private $enableCodeExchangeProof = false;
+    private $requireCodeChallengeForPublicClients = true;
+
+    /**
+     * @var CodeChallengeVerifierInterface[]
+     */
+    private $codeChallengeVerifiers = [];
 
     /**
      * @param AuthCodeRepositoryInterface     $authCodeRepository
@@ -53,11 +61,22 @@ class AuthCodeGrant extends AbstractAuthorizeGrant
         $this->setRefreshTokenRepository($refreshTokenRepository);
         $this->authCodeTTL = $authCodeTTL;
         $this->refreshTokenTTL = new DateInterval('P1M');
+
+        if (in_array('sha256', hash_algos(), true)) {
+            $s256Verifier = new S256Verifier();
+            $this->codeChallengeVerifiers[$s256Verifier->getMethod()] = $s256Verifier;
+        }
+
+        $plainVerifier = new PlainVerifier();
+        $this->codeChallengeVerifiers[$plainVerifier->getMethod()] = $plainVerifier;
     }
 
-    public function enableCodeExchangeProof()
+    /**
+     * Disable the requirement for a code challenge for public clients.
+     */
+    public function disableRequireCodeChallengeForPublicClients()
     {
-        $this->enableCodeExchangeProof = true;
+        $this->requireCodeChallengeForPublicClients = false;
     }
 
     /**
@@ -76,8 +95,15 @@ class AuthCodeGrant extends AbstractAuthorizeGrant
         ResponseTypeInterface $responseType,
         DateInterval $accessTokenTTL
     ) {
-        // Validate request
-        $client = $this->validateClient($request);
+        list($clientId) = $this->getClientCredentials($request);
+
+        $client = $this->getClientEntityOrFail($clientId, $request);
+
+        // Only validate the client if it is confidential
+        if ($client->isConfidential()) {
+            $this->validateClient($request);
+        }
+
         $encryptedAuthCode = $this->getRequestParameter('code', $request, null);
 
         if ($encryptedAuthCode === null) {
@@ -100,7 +126,7 @@ class AuthCodeGrant extends AbstractAuthorizeGrant
         }
 
         // Validate code challenge
-        if ($this->enableCodeExchangeProof === true) {
+        if (!empty($authCodePayload->code_challenge)) {
             $codeVerifier = $this->getRequestParameter('code_verifier', $request, null);
 
             if ($codeVerifier === null) {
@@ -116,32 +142,21 @@ class AuthCodeGrant extends AbstractAuthorizeGrant
                 );
             }
 
-            switch ($authCodePayload->code_challenge_method) {
-                case 'plain':
-                    if (hash_equals($codeVerifier, $authCodePayload->code_challenge) === false) {
-                        throw OAuthServerException::invalidGrant('Failed to verify `code_verifier`.');
-                    }
+            if (property_exists($authCodePayload, 'code_challenge_method')) {
+                if (isset($this->codeChallengeVerifiers[$authCodePayload->code_challenge_method])) {
+                    $codeChallengeVerifier = $this->codeChallengeVerifiers[$authCodePayload->code_challenge_method];
 
-                    break;
-                case 'S256':
-                    if (
-                        hash_equals(
-                            strtr(rtrim(base64_encode(hash('sha256', $codeVerifier, true)), '='), '+/', '-_'),
-                            $authCodePayload->code_challenge
-                        ) === false
-                    ) {
+                    if ($codeChallengeVerifier->verifyCodeChallenge($codeVerifier, $authCodePayload->code_challenge) === false) {
                         throw OAuthServerException::invalidGrant('Failed to verify `code_verifier`.');
                     }
-                    // @codeCoverageIgnoreStart
-                    break;
-                default:
+                } else {
                     throw OAuthServerException::serverError(
                         sprintf(
                             'Unsupported code challenge method `%s`',
                             $authCodePayload->code_challenge_method
                         )
                     );
-                // @codeCoverageIgnoreEnd
+                }
             }
         }
 
@@ -236,17 +251,7 @@ class AuthCodeGrant extends AbstractAuthorizeGrant
             throw OAuthServerException::invalidRequest('client_id');
         }
 
-        $client = $this->clientRepository->getClientEntity(
-            $clientId,
-            $this->getIdentifier(),
-            null,
-            false
-        );
-
-        if ($client instanceof ClientEntityInterface === false) {
-            $this->getEmitter()->emit(new RequestEvent(RequestEvent::CLIENT_AUTHENTICATION_FAILED, $request));
-            throw OAuthServerException::invalidClient();
-        }
+        $client = $this->getClientEntityOrFail($clientId, $request);
 
         $redirectUri = $this->getQueryStringParameter('redirect_uri', $request);
 
@@ -255,7 +260,7 @@ class AuthCodeGrant extends AbstractAuthorizeGrant
         } elseif (empty($client->getRedirectUri()) ||
             (\is_array($client->getRedirectUri()) && \count($client->getRedirectUri()) !== 1)) {
             $this->getEmitter()->emit(new RequestEvent(RequestEvent::CLIENT_AUTHENTICATION_FAILED, $request));
-            throw OAuthServerException::invalidClient();
+            throw OAuthServerException::invalidClient($request);
         } else {
             $redirectUri = \is_array($client->getRedirectUri())
                 ? $client->getRedirectUri()[0]
@@ -280,18 +285,20 @@ class AuthCodeGrant extends AbstractAuthorizeGrant
 
         $authorizationRequest->setScopes($scopes);
 
-        if ($this->enableCodeExchangeProof === true) {
-            $codeChallenge = $this->getQueryStringParameter('code_challenge', $request);
-            if ($codeChallenge === null) {
-                throw OAuthServerException::invalidRequest('code_challenge');
-            }
+        $codeChallenge = $this->getQueryStringParameter('code_challenge', $request);
 
+        if ($codeChallenge !== null) {
             $codeChallengeMethod = $this->getQueryStringParameter('code_challenge_method', $request, 'plain');
 
-            if (\in_array($codeChallengeMethod, ['plain', 'S256'], true) === false) {
+            if (array_key_exists($codeChallengeMethod, $this->codeChallengeVerifiers) === false) {
                 throw OAuthServerException::invalidRequest(
                     'code_challenge_method',
-                    'Code challenge method must be `plain` or `S256`'
+                    'Code challenge method must be one of ' . implode(', ', array_map(
+                        function ($method) {
+                            return '`' . $method . '`';
+                        },
+                        array_keys($this->codeChallengeVerifiers)
+                    ))
                 );
             }
 
@@ -306,6 +313,8 @@ class AuthCodeGrant extends AbstractAuthorizeGrant
 
             $authorizationRequest->setCodeChallenge($codeChallenge);
             $authorizationRequest->setCodeChallengeMethod($codeChallengeMethod);
+        } elseif ($this->requireCodeChallengeForPublicClients && !$client->isConfidential()) {
+            throw OAuthServerException::invalidRequest('code_challenge', 'Code challenge must be provided for public clients');
         }
 
         return $authorizationRequest;
@@ -339,21 +348,23 @@ class AuthCodeGrant extends AbstractAuthorizeGrant
                 'auth_code_id'          => $authCode->getIdentifier(),
                 'scopes'                => $authCode->getScopes(),
                 'user_id'               => $authCode->getUserIdentifier(),
-                'expire_time'           => (new DateTime())->add($this->authCodeTTL)->format('U'),
+                'expire_time'           => (new DateTimeImmutable())->add($this->authCodeTTL)->getTimestamp(),
                 'code_challenge'        => $authorizationRequest->getCodeChallenge(),
                 'code_challenge_method' => $authorizationRequest->getCodeChallengeMethod(),
             ];
 
+            $jsonPayload = json_encode($payload);
+
+            if ($jsonPayload === false) {
+                throw new LogicException('An error was encountered when JSON encoding the authorization request response');
+            }
+
             $response = new RedirectResponse();
             $response->setRedirectUri(
                 $this->makeRedirectUri(
                     $finalRedirectUri,
                     [
-                        'code'  => $this->encrypt(
-                            json_encode(
-                                $payload
-                            )
-                        ),
+                        'code'  => $this->encrypt($jsonPayload),
                         'state' => $authorizationRequest->getState(),
                     ]
                 )
diff --git a/src/Grant/ImplicitGrant.php b/src/Grant/ImplicitGrant.php
index 63a6c0b2..251ea6c2 100644
--- a/src/Grant/ImplicitGrant.php
+++ b/src/Grant/ImplicitGrant.php
@@ -10,8 +10,6 @@
 namespace League\OAuth2\Server\Grant;
 
 use DateInterval;
-use DateTime;
-use League\OAuth2\Server\Entities\ClientEntityInterface;
 use League\OAuth2\Server\Entities\UserEntityInterface;
 use League\OAuth2\Server\Exception\OAuthServerException;
 use League\OAuth2\Server\Repositories\RefreshTokenRepositoryInterface;
@@ -126,17 +124,7 @@ class ImplicitGrant extends AbstractAuthorizeGrant
             throw OAuthServerException::invalidRequest('client_id');
         }
 
-        $client = $this->clientRepository->getClientEntity(
-            $clientId,
-            $this->getIdentifier(),
-            null,
-            false
-        );
-
-        if ($client instanceof ClientEntityInterface === false) {
-            $this->getEmitter()->emit(new RequestEvent(RequestEvent::CLIENT_AUTHENTICATION_FAILED, $request));
-            throw OAuthServerException::invalidClient();
-        }
+        $client = $this->getClientEntityOrFail($clientId, $request);
 
         $redirectUri = $this->getQueryStringParameter('redirect_uri', $request);
 
@@ -145,7 +133,7 @@ class ImplicitGrant extends AbstractAuthorizeGrant
         } elseif (is_array($client->getRedirectUri()) && count($client->getRedirectUri()) !== 1
             || empty($client->getRedirectUri())) {
             $this->getEmitter()->emit(new RequestEvent(RequestEvent::CLIENT_AUTHENTICATION_FAILED, $request));
-            throw OAuthServerException::invalidClient();
+            throw OAuthServerException::invalidClient($request);
         } else {
             $redirectUri = is_array($client->getRedirectUri())
                 ? $client->getRedirectUri()[0]
@@ -210,9 +198,9 @@ class ImplicitGrant extends AbstractAuthorizeGrant
                 $this->makeRedirectUri(
                     $finalRedirectUri,
                     [
-                        'access_token' => (string) $accessToken->convertToJWT($this->privateKey),
+                        'access_token' => (string) $accessToken,
                         'token_type'   => 'Bearer',
-                        'expires_in'   => $accessToken->getExpiryDateTime()->getTimestamp() - (new DateTime())->getTimestamp(),
+                        'expires_in'   => $accessToken->getExpiryDateTime()->getTimestamp() - \time(),
                         'state'        => $authorizationRequest->getState(),
                     ],
                     $this->queryDelimiter
diff --git a/src/Grant/PasswordGrant.php b/src/Grant/PasswordGrant.php
index cb53ccd8..0dc687b9 100644
--- a/src/Grant/PasswordGrant.php
+++ b/src/Grant/PasswordGrant.php
@@ -83,11 +83,13 @@ class PasswordGrant extends AbstractGrant
     protected function validateUser(ServerRequestInterface $request, ClientEntityInterface $client)
     {
         $username = $this->getRequestParameter('username', $request);
+
         if (is_null($username)) {
             throw OAuthServerException::invalidRequest('username');
         }
 
         $password = $this->getRequestParameter('password', $request);
+
         if (is_null($password)) {
             throw OAuthServerException::invalidRequest('password');
         }
@@ -98,10 +100,11 @@ class PasswordGrant extends AbstractGrant
             $this->getIdentifier(),
             $client
         );
+
         if ($user instanceof UserEntityInterface === false) {
             $this->getEmitter()->emit(new RequestEvent(RequestEvent::USER_AUTHENTICATION_FAILED, $request));
 
-            throw OAuthServerException::invalidCredentials();
+            throw OAuthServerException::invalidGrant();
         }
 
         return $user;
diff --git a/src/Repositories/ClientRepositoryInterface.php b/src/Repositories/ClientRepositoryInterface.php
index ba0610d5..7eef494f 100644
--- a/src/Repositories/ClientRepositoryInterface.php
+++ b/src/Repositories/ClientRepositoryInterface.php
@@ -19,13 +19,20 @@ interface ClientRepositoryInterface extends RepositoryInterface
     /**
      * Get a client.
      *
-     * @param string      $clientIdentifier   The client's identifier
-     * @param null|string $grantType          The grant type used (if sent)
-     * @param null|string $clientSecret       The client's secret (if sent)
-     * @param bool        $mustValidateSecret If true the client must attempt to validate the secret if the client
-     *                                        is confidential
+     * @param string $clientIdentifier The client's identifier
      *
-     * @return ClientEntityInterface
+     * @return ClientEntityInterface|null
      */
-    public function getClientEntity($clientIdentifier, $grantType = null, $clientSecret = null, $mustValidateSecret = true);
+    public function getClientEntity($clientIdentifier);
+
+    /**
+     * Validate a client's secret.
+     *
+     * @param string      $clientIdentifier The client's identifier
+     * @param null|string $clientSecret     The client's secret (if sent)
+     * @param null|string $grantType        The type of grant the client is using (if sent)
+     *
+     * @return bool
+     */
+    public function validateClient($clientIdentifier, $clientSecret, $grantType);
 }
diff --git a/src/Repositories/ScopeRepositoryInterface.php b/src/Repositories/ScopeRepositoryInterface.php
index 52db05de..997aac2c 100644
--- a/src/Repositories/ScopeRepositoryInterface.php
+++ b/src/Repositories/ScopeRepositoryInterface.php
@@ -22,7 +22,7 @@ interface ScopeRepositoryInterface extends RepositoryInterface
      *
      * @param string $identifier The scope identifier
      *
-     * @return ScopeEntityInterface
+     * @return ScopeEntityInterface|null
      */
     public function getScopeEntityByIdentifier($identifier);
 
diff --git a/src/Repositories/UserRepositoryInterface.php b/src/Repositories/UserRepositoryInterface.php
index 0a9efef0..8ad49aa7 100644
--- a/src/Repositories/UserRepositoryInterface.php
+++ b/src/Repositories/UserRepositoryInterface.php
@@ -22,7 +22,7 @@ interface UserRepositoryInterface extends RepositoryInterface
      * @param string                $grantType    The grant type used
      * @param ClientEntityInterface $clientEntity
      *
-     * @return UserEntityInterface
+     * @return UserEntityInterface|null
      */
     public function getUserEntityByUserCredentials(
         $username,
diff --git a/src/RequestTypes/AuthorizationRequest.php b/src/RequestTypes/AuthorizationRequest.php
index 5faa45d4..6441e144 100644
--- a/src/RequestTypes/AuthorizationRequest.php
+++ b/src/RequestTypes/AuthorizationRequest.php
@@ -111,7 +111,7 @@ class AuthorizationRequest
     }
 
     /**
-     * @return UserEntityInterface
+     * @return UserEntityInterface|null
      */
     public function getUser()
     {
diff --git a/src/ResponseTypes/BearerTokenResponse.php b/src/ResponseTypes/BearerTokenResponse.php
index 4f6e9b47..f24a9485 100644
--- a/src/ResponseTypes/BearerTokenResponse.php
+++ b/src/ResponseTypes/BearerTokenResponse.php
@@ -11,9 +11,9 @@
 
 namespace League\OAuth2\Server\ResponseTypes;
 
-use DateTime;
 use League\OAuth2\Server\Entities\AccessTokenEntityInterface;
 use League\OAuth2\Server\Entities\RefreshTokenEntityInterface;
+use LogicException;
 use Psr\Http\Message\ResponseInterface;
 
 class BearerTokenResponse extends AbstractResponseType
@@ -25,32 +25,34 @@ class BearerTokenResponse extends AbstractResponseType
     {
         $expireDateTime = $this->accessToken->getExpiryDateTime()->getTimestamp();
 
-        $jwtAccessToken = $this->accessToken->convertToJWT($this->privateKey);
-
         $responseParams = [
             'token_type'   => 'Bearer',
-            'expires_in'   => $expireDateTime - (new DateTime())->getTimestamp(),
-            'access_token' => (string) $jwtAccessToken,
+            'expires_in'   => $expireDateTime - \time(),
+            'access_token' => (string) $this->accessToken,
         ];
 
         if ($this->refreshToken instanceof RefreshTokenEntityInterface) {
-            $refreshToken = $this->encrypt(
-                json_encode(
-                    [
-                        'client_id'        => $this->accessToken->getClient()->getIdentifier(),
-                        'refresh_token_id' => $this->refreshToken->getIdentifier(),
-                        'access_token_id'  => $this->accessToken->getIdentifier(),
-                        'scopes'           => $this->accessToken->getScopes(),
-                        'user_id'          => $this->accessToken->getUserIdentifier(),
-                        'expire_time'      => $this->refreshToken->getExpiryDateTime()->getTimestamp(),
-                    ]
-                )
-            );
+            $refreshTokenPayload = json_encode([
+                'client_id'        => $this->accessToken->getClient()->getIdentifier(),
+                'refresh_token_id' => $this->refreshToken->getIdentifier(),
+                'access_token_id'  => $this->accessToken->getIdentifier(),
+                'scopes'           => $this->accessToken->getScopes(),
+                'user_id'          => $this->accessToken->getUserIdentifier(),
+                'expire_time'      => $this->refreshToken->getExpiryDateTime()->getTimestamp(),
+            ]);
 
-            $responseParams['refresh_token'] = $refreshToken;
+            if ($refreshTokenPayload === false) {
+                throw new LogicException('Error encountered JSON encoding the refresh token payload');
+            }
+
+            $responseParams['refresh_token'] = $this->encrypt($refreshTokenPayload);
         }
 
-        $responseParams = array_merge($this->getExtraParams($this->accessToken), $responseParams);
+        $responseParams = json_encode(array_merge($this->getExtraParams($this->accessToken), $responseParams));
+
+        if ($responseParams === false) {
+            throw new LogicException('Error encountered JSON encoding response parameters');
+        }
 
         $response = $response
             ->withStatus(200)
@@ -58,7 +60,7 @@ class BearerTokenResponse extends AbstractResponseType
             ->withHeader('cache-control', 'no-store')
             ->withHeader('content-type', 'application/json; charset=UTF-8');
 
-        $response->getBody()->write(json_encode($responseParams));
+        $response->getBody()->write($responseParams);
 
         return $response;
     }
diff --git a/tests/AuthorizationServerTest.php b/tests/AuthorizationServerTest.php
index 0a8bf6d1..bcd87b5b 100644
--- a/tests/AuthorizationServerTest.php
+++ b/tests/AuthorizationServerTest.php
@@ -2,6 +2,7 @@
 
 namespace LeagueTests;
 
+use DateInterval;
 use League\OAuth2\Server\AuthorizationServer;
 use League\OAuth2\Server\CryptKey;
 use League\OAuth2\Server\Exception\OAuthServerException;
@@ -30,7 +31,7 @@ class AuthorizationServerTest extends TestCase
 {
     const DEFAULT_SCOPE = 'basic';
 
-    public function setUp()
+    public function setUp(): void
     {
         // Make sure the keys have the correct permissions.
         chmod(__DIR__ . '/Stubs/private.key', 0600);
@@ -49,7 +50,7 @@ class AuthorizationServerTest extends TestCase
             new StubResponseType()
         );
 
-        $server->enableGrantType(new ClientCredentialsGrant(), new \DateInterval('PT1M'));
+        $server->enableGrantType(new ClientCredentialsGrant(), new DateInterval('PT1M'));
 
         try {
             $server->respondToAccessTokenRequest(ServerRequestFactory::fromGlobals(), new Response);
@@ -82,7 +83,7 @@ class AuthorizationServerTest extends TestCase
         );
 
         $server->setDefaultScope(self::DEFAULT_SCOPE);
-        $server->enableGrantType(new ClientCredentialsGrant(), new \DateInterval('PT1M'));
+        $server->enableGrantType(new ClientCredentialsGrant(), new DateInterval('PT1M'));
 
         $_POST['grant_type'] = 'client_credentials';
         $_POST['client_id'] = 'foo';
@@ -116,35 +117,31 @@ class AuthorizationServerTest extends TestCase
         $privateKey = 'file://' . __DIR__ . '/Stubs/private.key';
         $encryptionKey = 'file://' . __DIR__ . '/Stubs/public.key';
 
-        $server = new class($clientRepository, $this->getMockBuilder(AccessTokenRepositoryInterface::class)->getMock(), $this->getMockBuilder(ScopeRepositoryInterface::class)->getMock(), $privateKey, $encryptionKey) extends AuthorizationServer {
-            protected function getResponseType()
-            {
-                $this->responseType = new class extends BearerTokenResponse {
-                    /* @return null|CryptKey */
-                    public function getPrivateKey()
-                    {
-                        return $this->privateKey;
-                    }
-
-                    public function getEncryptionKey()
-                    {
-                        return $this->encryptionKey;
-                    }
-                };
-
-                return parent::getResponseType();
-            }
-        };
+        $server = new AuthorizationServer(
+            $clientRepository,
+            $this->getMockBuilder(AccessTokenRepositoryInterface::class)->getMock(),
+            $this->getMockBuilder(ScopeRepositoryInterface::class)->getMock(),
+            'file://' . __DIR__ . '/Stubs/private.key',
+            'file://' . __DIR__ . '/Stubs/public.key'
+        );
 
         $abstractGrantReflection = new \ReflectionClass($server);
         $method = $abstractGrantReflection->getMethod('getResponseType');
         $method->setAccessible(true);
+
         $responseType = $method->invoke($server);
 
-        $this->assertInstanceOf(BearerTokenResponse::class, $responseType);
+        $responseTypeReflection = new \ReflectionClass($responseType);
+
+        $privateKeyProperty = $responseTypeReflection->getProperty('privateKey');
+        $privateKeyProperty->setAccessible(true);
+
+        $encryptionKeyProperty = $responseTypeReflection->getProperty('encryptionKey');
+        $encryptionKeyProperty->setAccessible(true);
+
         // generated instances should have keys setup
-        $this->assertSame($privateKey, $responseType->getPrivateKey()->getKeyPath());
-        $this->assertSame($encryptionKey, $responseType->getEncryptionKey());
+        $this->assertSame($privateKey, $privateKeyProperty->getValue($responseType)->getKeyPath());
+        $this->assertSame($encryptionKey, $encryptionKeyProperty->getValue($responseType));
     }
 
     public function testMultipleRequestsGetDifferentResponseTypeInstances()
@@ -217,7 +214,7 @@ class AuthorizationServerTest extends TestCase
         $grant = new AuthCodeGrant(
             $authCodeRepository,
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
 
         $server->enableGrantType($grant);
@@ -238,6 +235,7 @@ class AuthorizationServerTest extends TestCase
     {
         $client = new ClientEntity();
         $client->setRedirectUri('http://foo/bar');
+        $client->setConfidential();
         $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
         $clientRepositoryMock->method('getClientEntity')->willReturn($client);
 
@@ -248,7 +246,7 @@ class AuthorizationServerTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setClientRepository($clientRepositoryMock);
 
@@ -289,7 +287,7 @@ class AuthorizationServerTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setClientRepository($clientRepositoryMock);
 
@@ -324,10 +322,6 @@ class AuthorizationServerTest extends TestCase
         }
     }
 
-    /**
-     * @expectedException  \League\OAuth2\Server\Exception\OAuthServerException
-     * @expectedExceptionCode 2
-     */
     public function testValidateAuthorizationRequestUnregistered()
     {
         $server = new AuthorizationServer(
@@ -338,19 +332,13 @@ class AuthorizationServerTest extends TestCase
             'file://' . __DIR__ . '/Stubs/public.key'
         );
 
-        $request = new ServerRequest(
-            [],
-            [],
-            null,
-            null,
-            'php://input',
-            $headers = [],
-            $cookies = [],
-            $queryParams = [
-                'response_type' => 'code',
-                'client_id'     => 'foo',
-            ]
-        );
+        $request = (new ServerRequest())->withQueryParams([
+            'response_type' => 'code',
+            'client_id' => 'foo',
+        ]);
+
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
+        $this->expectExceptionCode(2);
 
         $server->validateAuthorizationRequest($request);
     }
diff --git a/tests/AuthorizationValidators/BearerTokenValidatorTest.php b/tests/AuthorizationValidators/BearerTokenValidatorTest.php
index 801846cb..69e56995 100644
--- a/tests/AuthorizationValidators/BearerTokenValidatorTest.php
+++ b/tests/AuthorizationValidators/BearerTokenValidatorTest.php
@@ -11,10 +11,6 @@ use Zend\Diactoros\ServerRequest;
 
 class BearerTokenValidatorTest extends TestCase
 {
-    /**
-     * @expectedException League\OAuth2\Server\Exception\OAuthServerException
-     * @expectedExceptionCode 9
-     */
     public function testThrowExceptionWhenAccessTokenIsNotSigned()
     {
         $accessTokenRepositoryMock = $this->getMockBuilder(AccessTokenRepositoryInterface::class)->getMock();
@@ -32,8 +28,10 @@ class BearerTokenValidatorTest extends TestCase
             ->set('scopes', 'scope1 scope2 scope3 scope4')
             ->getToken();
 
-        $request = new ServerRequest();
-        $request = $request->withHeader('authorization', sprintf('Bearer %s', $unsignedJwt));
+        $request = (new ServerRequest())->withHeader('authorization', sprintf('Bearer %s', $unsignedJwt));
+
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
+        $this->expectExceptionCode(9);
 
         $bearerTokenValidator->validateAuthorization($request);
     }
diff --git a/tests/CodeChallengeVerifiers/PlainVerifierTest.php b/tests/CodeChallengeVerifiers/PlainVerifierTest.php
new file mode 100644
index 00000000..437c0c2f
--- /dev/null
+++ b/tests/CodeChallengeVerifiers/PlainVerifierTest.php
@@ -0,0 +1,24 @@
+<?php
+
+namespace LeagueTests\CodeChallengeVerifiers;
+
+use League\OAuth2\Server\CodeChallengeVerifiers\PlainVerifier;
+use PHPUnit\Framework\TestCase;
+
+class PlainVerifierTest extends TestCase
+{
+    public function testGetMethod()
+    {
+        $verifier = new PlainVerifier();
+
+        $this->assertEquals('plain', $verifier->getMethod());
+    }
+
+    public function testVerifyCodeChallenge()
+    {
+        $verifier = new PlainVerifier();
+
+        $this->assertTrue($verifier->verifyCodeChallenge('foo', 'foo'));
+        $this->assertFalse($verifier->verifyCodeChallenge('foo', 'bar'));
+    }
+}
diff --git a/tests/CodeChallengeVerifiers/S256VerifierTest.php b/tests/CodeChallengeVerifiers/S256VerifierTest.php
new file mode 100644
index 00000000..cb96c000
--- /dev/null
+++ b/tests/CodeChallengeVerifiers/S256VerifierTest.php
@@ -0,0 +1,37 @@
+<?php
+
+namespace LeagueTests\CodeChallengeVerifiers;
+
+use League\OAuth2\Server\CodeChallengeVerifiers\S256Verifier;
+use PHPUnit\Framework\TestCase;
+
+class S256VerifierTest extends TestCase
+{
+    public function testGetMethod()
+    {
+        $verifier = new S256Verifier();
+
+        $this->assertEquals('S256', $verifier->getMethod());
+    }
+
+    public function testVerifyCodeChallengeSucceeds()
+    {
+        $codeChallenge = $this->createCodeChallenge('foo');
+        $verifier = new S256Verifier();
+
+        $this->assertTrue($verifier->verifyCodeChallenge('foo', $codeChallenge));
+    }
+
+    public function testVerifyCodeChallengeFails()
+    {
+        $codeChallenge = $this->createCodeChallenge('bar');
+        $verifier = new S256Verifier();
+
+        $this->assertFalse($verifier->verifyCodeChallenge('foo', $codeChallenge));
+    }
+
+    private function createCodeChallenge($codeVerifier)
+    {
+        return strtr(rtrim(base64_encode(hash('sha256', $codeVerifier, true)), '='), '+/', '-_');
+    }
+}
diff --git a/tests/Exception/OAuthServerExceptionTest.php b/tests/Exception/OAuthServerExceptionTest.php
index 201fb5dd..eb2b2ad3 100644
--- a/tests/Exception/OAuthServerExceptionTest.php
+++ b/tests/Exception/OAuthServerExceptionTest.php
@@ -4,10 +4,68 @@ namespace LeagueTests\Exception;
 
 use Exception;
 use League\OAuth2\Server\Exception\OAuthServerException;
+use League\OAuth2\Server\Grant\AbstractGrant;
+use League\OAuth2\Server\Repositories\ClientRepositoryInterface;
 use PHPUnit\Framework\TestCase;
+use Zend\Diactoros\Response;
+use Zend\Diactoros\ServerRequest;
 
 class OAuthServerExceptionTest extends TestCase
 {
+    public function testInvalidClientExceptionSetsAuthenticateHeader()
+    {
+        $serverRequest = (new ServerRequest())
+            ->withParsedBody([
+                'client_id' => 'foo',
+            ])
+            ->withAddedHeader('Authorization', 'Basic fakeauthdetails');
+
+        try {
+            $this->issueInvalidClientException($serverRequest);
+        } catch (OAuthServerException $e) {
+            $response = $e->generateHttpResponse(new Response());
+
+            $this->assertTrue($response->hasHeader('WWW-Authenticate'));
+        }
+    }
+
+    public function testInvalidClientExceptionOmitsAuthenticateHeader()
+    {
+        $serverRequest = (new ServerRequest())
+            ->withParsedBody([
+                'client_id' => 'foo',
+            ]);
+
+        try {
+            $this->issueInvalidClientException($serverRequest);
+        } catch (OAuthServerException $e) {
+            $response = $e->generateHttpResponse(new Response());
+
+            $this->assertFalse($response->hasHeader('WWW-Authenticate'));
+        }
+    }
+
+    /**
+     * Issue an invalid client exception
+     *
+     * @throws OAuthServerException
+     */
+    private function issueInvalidClientException($serverRequest)
+    {
+        $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
+        $clientRepositoryMock->method('validateClient')->willReturn(false);
+
+        $grantMock = $this->getMockForAbstractClass(AbstractGrant::class);
+        $grantMock->setClientRepository($clientRepositoryMock);
+
+        $abstractGrantReflection = new \ReflectionClass($grantMock);
+
+        $validateClientMethod = $abstractGrantReflection->getMethod('validateClient');
+        $validateClientMethod->setAccessible(true);
+
+        $validateClientMethod->invoke($grantMock, $serverRequest);
+    }
+
     public function testHasRedirect()
     {
         $exceptionWithRedirect = OAuthServerException::accessDenied('some hint', 'https://example.com/error');
@@ -27,7 +85,9 @@ class OAuthServerExceptionTest extends TestCase
         $previous = new Exception('This is the previous');
         $exceptionWithPrevious = OAuthServerException::accessDenied(null, null, $previous);
 
-        $this->assertSame('This is the previous', $exceptionWithPrevious->getPrevious()->getMessage());
+        $previousMessage = $exceptionWithPrevious->getPrevious() !== null ? $exceptionWithPrevious->getPrevious()->getMessage() : null;
+
+        $this->assertSame('This is the previous', $previousMessage);
     }
 
     public function testDoesNotHavePrevious()
diff --git a/tests/Grant/AbstractGrantTest.php b/tests/Grant/AbstractGrantTest.php
index 75d3bcae..a4b94264 100644
--- a/tests/Grant/AbstractGrantTest.php
+++ b/tests/Grant/AbstractGrantTest.php
@@ -2,7 +2,8 @@
 
 namespace LeagueTests\Grant;
 
-use League\Event\Emitter;
+use DateInterval;
+use League\OAuth2\Server\CryptKey;
 use League\OAuth2\Server\Entities\AccessTokenEntityInterface;
 use League\OAuth2\Server\Entities\AuthCodeEntityInterface;
 use League\OAuth2\Server\Entities\RefreshTokenEntityInterface;
@@ -23,21 +24,13 @@ use Zend\Diactoros\ServerRequest;
 
 class AbstractGrantTest extends TestCase
 {
-    public function testGetSet()
-    {
-        /** @var AbstractGrant $grantMock */
-        $grantMock = $this->getMockForAbstractClass(AbstractGrant::class);
-        $grantMock->setEmitter(new Emitter());
-    }
-
     public function testHttpBasicWithPassword()
     {
         /** @var AbstractGrant $grantMock */
         $grantMock = $this->getMockForAbstractClass(AbstractGrant::class);
         $abstractGrantReflection = new \ReflectionClass($grantMock);
 
-        $serverRequest = new ServerRequest();
-        $serverRequest = $serverRequest->withHeader('Authorization', 'Basic ' . base64_encode('Open:Sesame'));
+        $serverRequest = (new ServerRequest())->withHeader('Authorization', 'Basic ' . base64_encode('Open:Sesame'));
         $basicAuthMethod = $abstractGrantReflection->getMethod('getBasicAuthCredentials');
         $basicAuthMethod->setAccessible(true);
 
@@ -50,8 +43,7 @@ class AbstractGrantTest extends TestCase
         $grantMock = $this->getMockForAbstractClass(AbstractGrant::class);
         $abstractGrantReflection = new \ReflectionClass($grantMock);
 
-        $serverRequest = new ServerRequest();
-        $serverRequest = $serverRequest->withHeader('Authorization', 'Basic ' . base64_encode('Open:'));
+        $serverRequest = (new ServerRequest())->withHeader('Authorization', 'Basic ' . base64_encode('Open:'));
         $basicAuthMethod = $abstractGrantReflection->getMethod('getBasicAuthCredentials');
         $basicAuthMethod->setAccessible(true);
 
@@ -64,8 +56,7 @@ class AbstractGrantTest extends TestCase
         $grantMock = $this->getMockForAbstractClass(AbstractGrant::class);
         $abstractGrantReflection = new \ReflectionClass($grantMock);
 
-        $serverRequest = new ServerRequest();
-        $serverRequest = $serverRequest->withHeader('Authorization', 'Foo ' . base64_encode('Open:Sesame'));
+        $serverRequest = (new ServerRequest())->withHeader('Authorization', 'Foo ' . base64_encode('Open:Sesame'));
         $basicAuthMethod = $abstractGrantReflection->getMethod('getBasicAuthCredentials');
         $basicAuthMethod->setAccessible(true);
 
@@ -78,8 +69,7 @@ class AbstractGrantTest extends TestCase
         $grantMock = $this->getMockForAbstractClass(AbstractGrant::class);
         $abstractGrantReflection = new \ReflectionClass($grantMock);
 
-        $serverRequest = new ServerRequest();
-        $serverRequest = $serverRequest->withHeader('Authorization', 'Basic ||');
+        $serverRequest = (new ServerRequest())->withHeader('Authorization', 'Basic ||');
         $basicAuthMethod = $abstractGrantReflection->getMethod('getBasicAuthCredentials');
         $basicAuthMethod->setAccessible(true);
 
@@ -92,8 +82,7 @@ class AbstractGrantTest extends TestCase
         $grantMock = $this->getMockForAbstractClass(AbstractGrant::class);
         $abstractGrantReflection = new \ReflectionClass($grantMock);
 
-        $serverRequest = new ServerRequest();
-        $serverRequest = $serverRequest->withHeader('Authorization', 'Basic ' . base64_encode('OpenSesame'));
+        $serverRequest = (new ServerRequest())->withHeader('Authorization', 'Basic ' . base64_encode('OpenSesame'));
         $basicAuthMethod = $abstractGrantReflection->getMethod('getBasicAuthCredentials');
         $basicAuthMethod->setAccessible(true);
 
@@ -113,16 +102,14 @@ class AbstractGrantTest extends TestCase
 
         $abstractGrantReflection = new \ReflectionClass($grantMock);
 
-        $serverRequest = new ServerRequest();
-        $serverRequest = $serverRequest->withParsedBody(
-            [
-                'client_id' => 'foo',
-            ]
-        );
+        $serverRequest = (new ServerRequest())->withParsedBody([
+            'client_id' => 'foo',
+        ]);
+
         $validateClientMethod = $abstractGrantReflection->getMethod('validateClient');
         $validateClientMethod->setAccessible(true);
 
-        $result = $validateClientMethod->invoke($grantMock, $serverRequest, true, true);
+        $result = $validateClientMethod->invoke($grantMock, $serverRequest);
         $this->assertEquals($client, $result);
     }
 
@@ -139,14 +126,12 @@ class AbstractGrantTest extends TestCase
 
         $abstractGrantReflection = new \ReflectionClass($grantMock);
 
-        $serverRequest = new ServerRequest();
-        $serverRequest = $serverRequest->withParsedBody(
-            [
-                'client_id'     => 'foo',
-                'client_secret' => 'bar',
-                'redirect_uri'  => 'http://foo/bar',
-            ]
-        );
+        $serverRequest = (new ServerRequest())->withParsedBody([
+            'client_id'     => 'foo',
+            'client_secret' => 'bar',
+            'redirect_uri'  => 'http://foo/bar',
+        ]);
+
         $validateClientMethod = $abstractGrantReflection->getMethod('validateClient');
         $validateClientMethod->setAccessible(true);
 
@@ -154,9 +139,6 @@ class AbstractGrantTest extends TestCase
         $this->assertEquals($client, $result);
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
-     */
     public function testValidateClientMissingClientId()
     {
         $client = new ClientEntity();
@@ -173,16 +155,15 @@ class AbstractGrantTest extends TestCase
         $validateClientMethod = $abstractGrantReflection->getMethod('validateClient');
         $validateClientMethod->setAccessible(true);
 
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
+
         $validateClientMethod->invoke($grantMock, $serverRequest, true, true);
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
-     */
     public function testValidateClientMissingClientSecret()
     {
         $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
-        $clientRepositoryMock->method('getClientEntity')->willReturn(null);
+        $clientRepositoryMock->method('validateClient')->willReturn(false);
 
         /** @var AbstractGrant $grantMock */
         $grantMock = $this->getMockForAbstractClass(AbstractGrant::class);
@@ -190,24 +171,22 @@ class AbstractGrantTest extends TestCase
 
         $abstractGrantReflection = new \ReflectionClass($grantMock);
 
-        $serverRequest = new ServerRequest();
-        $serverRequest = $serverRequest->withParsedBody([
+        $serverRequest = (new ServerRequest())->withParsedBody([
             'client_id' => 'foo',
         ]);
 
         $validateClientMethod = $abstractGrantReflection->getMethod('validateClient');
         $validateClientMethod->setAccessible(true);
 
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
+
         $validateClientMethod->invoke($grantMock, $serverRequest, true, true);
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
-     */
     public function testValidateClientInvalidClientSecret()
     {
         $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
-        $clientRepositoryMock->method('getClientEntity')->willReturn(null);
+        $clientRepositoryMock->method('validateClient')->willReturn(false);
 
         /** @var AbstractGrant $grantMock */
         $grantMock = $this->getMockForAbstractClass(AbstractGrant::class);
@@ -215,8 +194,7 @@ class AbstractGrantTest extends TestCase
 
         $abstractGrantReflection = new \ReflectionClass($grantMock);
 
-        $serverRequest = new ServerRequest();
-        $serverRequest = $serverRequest->withParsedBody([
+        $serverRequest = (new ServerRequest())->withParsedBody([
             'client_id'     => 'foo',
             'client_secret' => 'foo',
         ]);
@@ -224,12 +202,11 @@ class AbstractGrantTest extends TestCase
         $validateClientMethod = $abstractGrantReflection->getMethod('validateClient');
         $validateClientMethod->setAccessible(true);
 
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
+
         $validateClientMethod->invoke($grantMock, $serverRequest, true, true);
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
-     */
     public function testValidateClientInvalidRedirectUri()
     {
         $client = new ClientEntity();
@@ -243,8 +220,7 @@ class AbstractGrantTest extends TestCase
 
         $abstractGrantReflection = new \ReflectionClass($grantMock);
 
-        $serverRequest = new ServerRequest();
-        $serverRequest = $serverRequest->withParsedBody([
+        $serverRequest = (new ServerRequest())->withParsedBody([
             'client_id'    => 'foo',
             'redirect_uri' => 'http://bar/foo',
         ]);
@@ -252,12 +228,11 @@ class AbstractGrantTest extends TestCase
         $validateClientMethod = $abstractGrantReflection->getMethod('validateClient');
         $validateClientMethod->setAccessible(true);
 
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
+
         $validateClientMethod->invoke($grantMock, $serverRequest, true, true);
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
-     */
     public function testValidateClientInvalidRedirectUriArray()
     {
         $client = new ClientEntity();
@@ -271,8 +246,7 @@ class AbstractGrantTest extends TestCase
 
         $abstractGrantReflection = new \ReflectionClass($grantMock);
 
-        $serverRequest = new ServerRequest();
-        $serverRequest = $serverRequest->withParsedBody([
+        $serverRequest = (new ServerRequest())->withParsedBody([
             'client_id'    => 'foo',
             'redirect_uri' => 'http://bar/foo',
         ]);
@@ -280,16 +254,15 @@ class AbstractGrantTest extends TestCase
         $validateClientMethod = $abstractGrantReflection->getMethod('validateClient');
         $validateClientMethod->setAccessible(true);
 
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
+
         $validateClientMethod->invoke($grantMock, $serverRequest, true, true);
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
-     */
     public function testValidateClientBadClient()
     {
         $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
-        $clientRepositoryMock->method('getClientEntity')->willReturn(null);
+        $clientRepositoryMock->method('validateClient')->willReturn(false);
 
         /** @var AbstractGrant $grantMock */
         $grantMock = $this->getMockForAbstractClass(AbstractGrant::class);
@@ -297,8 +270,7 @@ class AbstractGrantTest extends TestCase
 
         $abstractGrantReflection = new \ReflectionClass($grantMock);
 
-        $serverRequest = new ServerRequest();
-        $serverRequest = $serverRequest->withParsedBody([
+        $serverRequest = (new ServerRequest())->withParsedBody([
             'client_id'     => 'foo',
             'client_secret' => 'bar',
         ]);
@@ -306,6 +278,8 @@ class AbstractGrantTest extends TestCase
         $validateClientMethod = $abstractGrantReflection->getMethod('validateClient');
         $validateClientMethod->setAccessible(true);
 
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
+
         $validateClientMethod->invoke($grantMock, $serverRequest, true);
     }
 
@@ -314,8 +288,7 @@ class AbstractGrantTest extends TestCase
         $grantMock = $this->getMockForAbstractClass(AbstractGrant::class);
         $grantMock->method('getIdentifier')->willReturn('foobar');
 
-        $serverRequest = new ServerRequest();
-        $serverRequest = $serverRequest->withParsedBody([
+        $serverRequest = (new ServerRequest())->withParsedBody([
             'grant_type' => 'foobar',
         ]);
 
@@ -332,7 +305,7 @@ class AbstractGrantTest extends TestCase
 
         /** @var AbstractGrant $grantMock */
         $grantMock = $this->getMockForAbstractClass(AbstractGrant::class);
-        $grantMock->setRefreshTokenTTL(new \DateInterval('PT1M'));
+        $grantMock->setRefreshTokenTTL(new DateInterval('PT1M'));
         $grantMock->setRefreshTokenRepository($refreshTokenRepoMock);
 
         $abstractGrantReflection = new \ReflectionClass($grantMock);
@@ -374,6 +347,7 @@ class AbstractGrantTest extends TestCase
 
         /** @var AbstractGrant $grantMock */
         $grantMock = $this->getMockForAbstractClass(AbstractGrant::class);
+        $grantMock->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
         $grantMock->setAccessTokenRepository($accessTokenRepoMock);
 
         $abstractGrantReflection = new \ReflectionClass($grantMock);
@@ -383,7 +357,7 @@ class AbstractGrantTest extends TestCase
         /** @var AccessTokenEntityInterface $accessToken */
         $accessToken = $issueAccessTokenMethod->invoke(
             $grantMock,
-            new \DateInterval('PT1H'),
+            new DateInterval('PT1H'),
             new ClientEntity(),
             123,
             [new ScopeEntity()]
@@ -408,7 +382,7 @@ class AbstractGrantTest extends TestCase
             AuthCodeEntityInterface::class,
             $issueAuthCodeMethod->invoke(
                 $grantMock,
-                new \DateInterval('PT1H'),
+                new DateInterval('PT1H'),
                 new ClientEntity(),
                 123,
                 'http://foo/bar',
@@ -426,8 +400,7 @@ class AbstractGrantTest extends TestCase
         $method = $abstractGrantReflection->getMethod('getCookieParameter');
         $method->setAccessible(true);
 
-        $serverRequest = new ServerRequest();
-        $serverRequest = $serverRequest->withCookieParams([
+        $serverRequest = (new ServerRequest())->withCookieParams([
             'foo' => 'bar',
         ]);
 
@@ -444,8 +417,7 @@ class AbstractGrantTest extends TestCase
         $method = $abstractGrantReflection->getMethod('getQueryStringParameter');
         $method->setAccessible(true);
 
-        $serverRequest = new ServerRequest();
-        $serverRequest = $serverRequest->withQueryParams([
+        $serverRequest = (new ServerRequest())->withQueryParams([
             'foo' => 'bar',
         ]);
 
@@ -466,9 +438,6 @@ class AbstractGrantTest extends TestCase
         $this->assertEquals([$scope], $grantMock->validateScopes('basic   '));
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
-     */
     public function testValidateScopesBadScope()
     {
         $scopeRepositoryMock = $this->getMockBuilder(ScopeRepositoryInterface::class)->getMock();
@@ -478,6 +447,8 @@ class AbstractGrantTest extends TestCase
         $grantMock = $this->getMockForAbstractClass(AbstractGrant::class);
         $grantMock->setScopeRepository($scopeRepositoryMock);
 
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
+
         $grantMock->validateScopes('basic   ');
     }
 
@@ -489,7 +460,7 @@ class AbstractGrantTest extends TestCase
         $method = $abstractGrantReflection->getMethod('generateUniqueIdentifier');
         $method->setAccessible(true);
 
-        $this->assertInternalType('string', $method->invoke($grantMock));
+        $this->assertIsString($method->invoke($grantMock));
     }
 
     public function testCanRespondToAuthorizationRequest()
@@ -498,21 +469,21 @@ class AbstractGrantTest extends TestCase
         $this->assertFalse($grantMock->canRespondToAuthorizationRequest(new ServerRequest()));
     }
 
-    /**
-     * @expectedException \LogicException
-     */
     public function testValidateAuthorizationRequest()
     {
         $grantMock = $this->getMockForAbstractClass(AbstractGrant::class);
+
+        $this->expectException(\LogicException::class);
+
         $grantMock->validateAuthorizationRequest(new ServerRequest());
     }
 
-    /**
-     * @expectedException \LogicException
-     */
     public function testCompleteAuthorizationRequest()
     {
         $grantMock = $this->getMockForAbstractClass(AbstractGrant::class);
+
+        $this->expectException(\LogicException::class);
+
         $grantMock->completeAuthorizationRequest(new AuthorizationRequest());
     }
 }
diff --git a/tests/Grant/AuthCodeGrantTest.php b/tests/Grant/AuthCodeGrantTest.php
index 04fb60c2..b2dc122a 100644
--- a/tests/Grant/AuthCodeGrantTest.php
+++ b/tests/Grant/AuthCodeGrantTest.php
@@ -2,6 +2,8 @@
 
 namespace LeagueTests\Grant;
 
+use DateInterval;
+use League\OAuth2\Server\CryptKey;
 use League\OAuth2\Server\Entities\AccessTokenEntityInterface;
 use League\OAuth2\Server\Entities\RefreshTokenEntityInterface;
 use League\OAuth2\Server\Exception\OAuthServerException;
@@ -38,9 +40,9 @@ class AuthCodeGrantTest extends TestCase
 
     const CODE_CHALLENGE = 'E9Melhoa2OwvFrEMTJguCHaoeK1t8URWbuGJSstw-cM';
 
-    public function setUp()
+    public function setUp(): void
     {
-        $this->cryptStub = new CryptTraitStub;
+        $this->cryptStub = new CryptTraitStub();
     }
 
     public function testGetIdentifier()
@@ -48,7 +50,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
 
         $this->assertEquals('authorization_code', $grant->getIdentifier());
@@ -59,7 +61,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
 
         $request = new ServerRequest(
@@ -83,6 +85,7 @@ class AuthCodeGrantTest extends TestCase
     {
         $client = new ClientEntity();
         $client->setRedirectUri('http://foo/bar');
+        $client->setConfidential();
 
         $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
         $clientRepositoryMock->method('getClientEntity')->willReturn($client);
@@ -94,7 +97,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setScopeRepository($scopeRepositoryMock);
@@ -122,6 +125,7 @@ class AuthCodeGrantTest extends TestCase
     {
         $client = new ClientEntity();
         $client->setRedirectUri(['http://foo/bar']);
+        $client->setConfidential();
         $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
         $clientRepositoryMock->method('getClientEntity')->willReturn($client);
 
@@ -132,7 +136,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setScopeRepository($scopeRepositoryMock);
@@ -170,9 +174,9 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
-        $grant->enableCodeExchangeProof();
+
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setScopeRepository($scopeRepositoryMock);
         $grant->setDefaultScope(self::DEFAULT_SCOPE);
@@ -196,9 +200,6 @@ class AuthCodeGrantTest extends TestCase
         $this->assertInstanceOf(AuthorizationRequest::class, $grant->validateAuthorizationRequest($request));
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
-     */
     public function testValidateAuthorizationRequestCodeChallengeInvalidLengthTooShort()
     {
         $client = new ClientEntity();
@@ -209,33 +210,23 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
-        $grant->enableCodeExchangeProof();
+
         $grant->setClientRepository($clientRepositoryMock);
 
-        $request = new ServerRequest(
-            [],
-            [],
-            null,
-            null,
-            'php://input',
-            [],
-            [],
-            [
-                'response_type'  => 'code',
-                'client_id'      => 'foo',
-                'redirect_uri'   => 'http://foo/bar',
-                'code_challenge' => str_repeat('A', 42),
-            ]
-        );
+        $request = (new ServerRequest())->withQueryParams([
+            'response_type'  => 'code',
+            'client_id'      => 'foo',
+            'redirect_uri'   => 'http://foo/bar',
+            'code_challenge' => str_repeat('A', 42),
+        ]);
+
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
 
         $grant->validateAuthorizationRequest($request);
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
-     */
     public function testValidateAuthorizationRequestCodeChallengeInvalidLengthTooLong()
     {
         $client = new ClientEntity();
@@ -246,33 +237,23 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
-        $grant->enableCodeExchangeProof();
+
         $grant->setClientRepository($clientRepositoryMock);
 
-        $request = new ServerRequest(
-            [],
-            [],
-            null,
-            null,
-            'php://input',
-            [],
-            [],
-            [
-                'response_type'  => 'code',
-                'client_id'      => 'foo',
-                'redirect_uri'   => 'http://foo/bar',
-                'code_challenge' => str_repeat('A', 129),
-            ]
-        );
+        $request = (new ServerRequest())->withQueryParams([
+            'response_type'  => 'code',
+            'client_id'      => 'foo',
+            'redirect_uri'   => 'http://foo/bar',
+            'code_challenge' => str_repeat('A', 129),
+        ]);
+
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
 
         $grant->validateAuthorizationRequest($request);
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
-     */
     public function testValidateAuthorizationRequestCodeChallengeInvalidCharacters()
     {
         $client = new ClientEntity();
@@ -283,34 +264,23 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
-        $grant->enableCodeExchangeProof();
+
         $grant->setClientRepository($clientRepositoryMock);
 
-        $request = new ServerRequest(
-            [],
-            [],
-            null,
-            null,
-            'php://input',
-            [],
-            [],
-            [
-                'response_type'  => 'code',
-                'client_id'      => 'foo',
-                'redirect_uri'   => 'http://foo/bar',
-                'code_challenge' => str_repeat('A', 42) . '!',
-            ]
-        );
+        $request = (new ServerRequest())->withQueryParams([
+            'response_type' => 'code',
+            'client_id' => 'foo',
+            'redirect_uri' => 'http://foo/bar',
+            'code_challenge' => str_repeat('A', 42) . '!',
+        ]);
+
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
 
         $grant->validateAuthorizationRequest($request);
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
-     * @expectedExceptionCode 3
-     */
     public function testValidateAuthorizationRequestMissingClientId()
     {
         $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
@@ -318,30 +288,20 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setClientRepository($clientRepositoryMock);
 
-        $request = new ServerRequest(
-            [],
-            [],
-            null,
-            null,
-            'php://input',
-            $headers = [],
-            $cookies = [],
-            $queryParams = [
-                'response_type' => 'code',
-            ]
-        );
+        $request = (new ServerRequest())->withQueryParams([
+            'response_type' => 'code',
+        ]);
+
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
+        $this->expectExceptionCode(3);
 
         $grant->validateAuthorizationRequest($request);
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
-     * @expectedExceptionCode 4
-     */
     public function testValidateAuthorizationRequestInvalidClientId()
     {
         $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
@@ -350,31 +310,21 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setClientRepository($clientRepositoryMock);
 
-        $request = new ServerRequest(
-            [],
-            [],
-            null,
-            null,
-            'php://input',
-            $headers = [],
-            $cookies = [],
-            $queryParams = [
-                'response_type' => 'code',
-                'client_id'     => 'foo',
-            ]
-        );
+        $request = (new ServerRequest())->withQueryParams([
+            'response_type' => 'code',
+            'client_id'     => 'foo',
+        ]);
+
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
+        $this->expectExceptionCode(4);
 
         $grant->validateAuthorizationRequest($request);
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
-     * @expectedExceptionCode 4
-     */
     public function testValidateAuthorizationRequestBadRedirectUriString()
     {
         $client = new ClientEntity();
@@ -385,32 +335,22 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setClientRepository($clientRepositoryMock);
 
-        $request = new ServerRequest(
-            [],
-            [],
-            null,
-            null,
-            'php://input',
-            [],
-            [],
-            [
-                'response_type' => 'code',
-                'client_id'     => 'foo',
-                'redirect_uri'  => 'http://bar',
-            ]
-        );
+        $request = (new ServerRequest())->withQueryParams([
+            'response_type' => 'code',
+            'client_id'     => 'foo',
+            'redirect_uri'  => 'http://bar',
+        ]);
+
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
+        $this->expectExceptionCode(4);
 
         $grant->validateAuthorizationRequest($request);
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
-     * @expectedExceptionCode 4
-     */
     public function testValidateAuthorizationRequestBadRedirectUriArray()
     {
         $client = new ClientEntity();
@@ -421,75 +361,22 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setClientRepository($clientRepositoryMock);
 
-        $request = new ServerRequest(
-            [],
-            [],
-            null,
-            null,
-            'php://input',
-            [],
-            [],
-            [
-                'response_type' => 'code',
-                'client_id'     => 'foo',
-                'redirect_uri'  => 'http://bar',
-            ]
-        );
+        $request = (new ServerRequest())->withQueryParams([
+            'response_type' => 'code',
+            'client_id'     => 'foo',
+            'redirect_uri'  => 'http://bar',
+        ]);
+
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
+        $this->expectExceptionCode(4);
 
         $grant->validateAuthorizationRequest($request);
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
-     * @expectedExceptionCode 3
-     */
-    public function testValidateAuthorizationRequestMissingCodeChallenge()
-    {
-        $client = new ClientEntity();
-        $client->setRedirectUri('http://foo/bar');
-        $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
-        $clientRepositoryMock->method('getClientEntity')->willReturn($client);
-
-        $scope = new ScopeEntity();
-        $scopeRepositoryMock = $this->getMockBuilder(ScopeRepositoryInterface::class)->getMock();
-        $scopeRepositoryMock->method('getScopeEntityByIdentifier')->willReturn($scope);
-
-        $grant = new AuthCodeGrant(
-            $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
-            $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
-        );
-        $grant->enableCodeExchangeProof();
-        $grant->setClientRepository($clientRepositoryMock);
-        $grant->setScopeRepository($scopeRepositoryMock);
-        $grant->setDefaultScope(self::DEFAULT_SCOPE);
-
-        $request = new ServerRequest(
-            [],
-            [],
-            null,
-            null,
-            'php://input',
-            [],
-            [],
-            [
-                'response_type' => 'code',
-                'client_id'     => 'foo',
-                'redirect_uri'  => 'http://foo/bar',
-            ]
-        );
-
-        $grant->validateAuthorizationRequest($request);
-    }
-
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
-     * @expectedExceptionCode 3
-     */
     public function testValidateAuthorizationRequestInvalidCodeChallengeMethod()
     {
         $client = new ClientEntity();
@@ -504,29 +391,23 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
-        $grant->enableCodeExchangeProof();
+
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setScopeRepository($scopeRepositoryMock);
         $grant->setDefaultScope(self::DEFAULT_SCOPE);
 
-        $request = new ServerRequest(
-            [],
-            [],
-            null,
-            null,
-            'php://input',
-            [],
-            [],
-            [
-                'response_type'         => 'code',
-                'client_id'             => 'foo',
-                'redirect_uri'          => 'http://foo/bar',
-                'code_challenge'        => 'foobar',
-                'code_challenge_method' => 'foo',
-            ]
-        );
+        $request = (new ServerRequest())->withQueryParams([
+            'response_type' => 'code',
+            'client_id' => 'foo',
+            'redirect_uri' => 'http://foo/bar',
+            'code_challenge' => 'foobar',
+            'code_challenge_method' => 'foo',
+        ]);
+
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
+        $this->expectExceptionCode(3);
 
         $grant->validateAuthorizationRequest($request);
     }
@@ -545,17 +426,13 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $authCodeRepository,
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setEncryptionKey($this->cryptStub->getKey());
 
         $this->assertInstanceOf(RedirectResponse::class, $grant->completeAuthorizationRequest($authRequest));
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
-     * @expectedExceptionCode 9
-     */
     public function testCompleteAuthorizationRequestDenied()
     {
         $authRequest = new AuthorizationRequest();
@@ -570,10 +447,13 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $authCodeRepository,
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setEncryptionKey($this->cryptStub->getKey());
 
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
+        $this->expectExceptionCode(9);
+
         $grant->completeAuthorizationRequest($authRequest);
     }
 
@@ -582,6 +462,7 @@ class AuthCodeGrantTest extends TestCase
         $client = new ClientEntity();
         $client->setIdentifier('foo');
         $client->setRedirectUri('http://foo/bar');
+        $client->setConfidential();
         $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
         $clientRepositoryMock->method('getClientEntity')->willReturn($client);
 
@@ -601,13 +482,14 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setScopeRepository($scopeRepositoryMock);
         $grant->setAccessTokenRepository($accessTokenRepositoryMock);
         $grant->setRefreshTokenRepository($refreshTokenRepositoryMock);
         $grant->setEncryptionKey($this->cryptStub->getKey());
+        $grant->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
 
         $request = new ServerRequest(
             [],
@@ -638,7 +520,140 @@ class AuthCodeGrantTest extends TestCase
         );
 
         /** @var StubResponseType $response */
-        $response = $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+        $response = $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
+
+        $this->assertInstanceOf(AccessTokenEntityInterface::class, $response->getAccessToken());
+        $this->assertInstanceOf(RefreshTokenEntityInterface::class, $response->getRefreshToken());
+    }
+
+    public function testRespondToAccessTokenRequestUsingHttpBasicAuth()
+    {
+        $client = new ClientEntity();
+        $client->setIdentifier('foo');
+        $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
+        $clientRepositoryMock->method('getClientEntity')->willReturn($client);
+
+        $scopeRepositoryMock = $this->getMockBuilder(ScopeRepositoryInterface::class)->getMock();
+        $scopeRepositoryMock->method('getScopeEntityByIdentifier')->willReturn(new ScopeEntity());
+        $scopeRepositoryMock->method('finalizeScopes')->willReturnArgument(0);
+
+        $accessTokenRepositoryMock = $this->getMockBuilder(AccessTokenRepositoryInterface::class)->getMock();
+        $accessTokenRepositoryMock->method('getNewToken')->willReturn(new AccessTokenEntity());
+
+        $refreshTokenRepositoryMock = $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock();
+        $refreshTokenRepositoryMock->method('getNewRefreshToken')->willReturn(new RefreshTokenEntity());
+
+        $authCodeGrant = new AuthCodeGrant(
+            $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
+            $refreshTokenRepositoryMock,
+            new \DateInterval('PT10M')
+        );
+
+        $authCodeGrant->setClientRepository($clientRepositoryMock);
+        $authCodeGrant->setScopeRepository($scopeRepositoryMock);
+        $authCodeGrant->setAccessTokenRepository($accessTokenRepositoryMock);
+        $authCodeGrant->setEncryptionKey($this->cryptStub->getKey());
+        $authCodeGrant->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
+
+        $request = new ServerRequest(
+            [],
+            [],
+            null,
+            'POST',
+            'php://input',
+            [
+                'Authorization' => 'Basic Zm9vOmJhcg==',
+            ],
+            [],
+            [],
+            [
+                'grant_type'   => 'authorization_code',
+                'redirect_uri' => 'http://foo/bar',
+                'code'         => $this->cryptStub->doEncrypt(
+                    json_encode(
+                        [
+                            'auth_code_id' => uniqid(),
+                            'client_id' => 'foo',
+                            'expire_time'  => time() + 3600,
+                            'user_id'      => 123,
+                            'scopes'       => ['foo'],
+                            'redirect_uri' => 'http://foo/bar',
+                        ]
+                    )
+                ),
+            ]
+        );
+
+        /** @var StubResponseType $response */
+        $response = $authCodeGrant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+
+        $this->assertInstanceOf(AccessTokenEntityInterface::class, $response->getAccessToken());
+        $this->assertInstanceOf(RefreshTokenEntityInterface::class, $response->getRefreshToken());
+    }
+
+    public function testRespondToAccessTokenRequestForPublicClient()
+    {
+        $client = new ClientEntity();
+        $client->setIdentifier('foo');
+        $client->setRedirectUri('http://foo/bar');
+        $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
+        $clientRepositoryMock->method('getClientEntity')->willReturn($client);
+
+        $scopeRepositoryMock = $this->getMockBuilder(ScopeRepositoryInterface::class)->getMock();
+        $scopeEntity = new ScopeEntity();
+        $scopeRepositoryMock->method('getScopeEntityByIdentifier')->willReturn($scopeEntity);
+        $scopeRepositoryMock->method('finalizeScopes')->willReturnArgument(0);
+
+        $accessTokenRepositoryMock = $this->getMockBuilder(AccessTokenRepositoryInterface::class)->getMock();
+        $accessTokenRepositoryMock->method('getNewToken')->willReturn(new AccessTokenEntity());
+        $accessTokenRepositoryMock->method('persistNewAccessToken')->willReturnSelf();
+
+        $refreshTokenRepositoryMock = $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock();
+        $refreshTokenRepositoryMock->method('persistNewRefreshToken')->willReturnSelf();
+        $refreshTokenRepositoryMock->method('getNewRefreshToken')->willReturn(new RefreshTokenEntity());
+
+        $grant = new AuthCodeGrant(
+            $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
+            $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
+            new DateInterval('PT10M')
+        );
+        $grant->setClientRepository($clientRepositoryMock);
+        $grant->setScopeRepository($scopeRepositoryMock);
+        $grant->setAccessTokenRepository($accessTokenRepositoryMock);
+        $grant->setRefreshTokenRepository($refreshTokenRepositoryMock);
+        $grant->setEncryptionKey($this->cryptStub->getKey());
+        $grant->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
+
+        $request = new ServerRequest(
+            [],
+            [],
+            null,
+            'POST',
+            'php://input',
+            [],
+            [],
+            [],
+            [
+                'grant_type'   => 'authorization_code',
+                'client_id'    => 'foo',
+                'redirect_uri' => 'http://foo/bar',
+                'code'         => $this->cryptStub->doEncrypt(
+                    json_encode(
+                        [
+                            'auth_code_id' => uniqid(),
+                            'expire_time'  => time() + 3600,
+                            'client_id'    => 'foo',
+                            'user_id'      => 123,
+                            'scopes'       => ['foo'],
+                            'redirect_uri' => 'http://foo/bar',
+                        ]
+                    )
+                ),
+            ]
+        );
+
+        /** @var StubResponseType $response */
+        $response = $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
 
         $this->assertInstanceOf(AccessTokenEntityInterface::class, $response->getAccessToken());
         $this->assertInstanceOf(RefreshTokenEntityInterface::class, $response->getRefreshToken());
@@ -675,6 +690,7 @@ class AuthCodeGrantTest extends TestCase
         $grant->setScopeRepository($scopeRepositoryMock);
         $grant->setAccessTokenRepository($accessTokenRepositoryMock);
         $grant->setEncryptionKey($this->cryptStub->getKey());
+        $grant->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
 
         $request = new ServerRequest(
             [],
@@ -716,6 +732,7 @@ class AuthCodeGrantTest extends TestCase
         $client = new ClientEntity();
         $client->setIdentifier('foo');
         $client->setRedirectUri('http://foo/bar');
+        $client->setConfidential();
         $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
         $clientRepositoryMock->method('getClientEntity')->willReturn($client);
 
@@ -735,14 +752,15 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
-        $grant->enableCodeExchangeProof();
+
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setScopeRepository($scopeRepositoryMock);
         $grant->setAccessTokenRepository($accessTokenRepositoryMock);
         $grant->setRefreshTokenRepository($refreshTokenRepositoryMock);
         $grant->setEncryptionKey($this->cryptStub->getKey());
+        $grant->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
 
         $request = new ServerRequest(
             [],
@@ -776,7 +794,7 @@ class AuthCodeGrantTest extends TestCase
         );
 
         /** @var StubResponseType $response */
-        $response = $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+        $response = $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
 
         $this->assertInstanceOf(AccessTokenEntityInterface::class, $response->getAccessToken());
         $this->assertInstanceOf(RefreshTokenEntityInterface::class, $response->getRefreshToken());
@@ -787,6 +805,7 @@ class AuthCodeGrantTest extends TestCase
         $client = new ClientEntity();
         $client->setIdentifier('foo');
         $client->setRedirectUri('http://foo/bar');
+        $client->setConfidential();
         $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
         $clientRepositoryMock->method('getClientEntity')->willReturn($client);
 
@@ -806,14 +825,15 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
-        $grant->enableCodeExchangeProof();
+
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setScopeRepository($scopeRepositoryMock);
         $grant->setAccessTokenRepository($accessTokenRepositoryMock);
         $grant->setRefreshTokenRepository($refreshTokenRepositoryMock);
         $grant->setEncryptionKey($this->cryptStub->getKey());
+        $grant->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
 
         $request = new ServerRequest(
             [],
@@ -847,27 +867,24 @@ class AuthCodeGrantTest extends TestCase
         );
 
         /** @var StubResponseType $response */
-        $response = $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+        $response = $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
 
         $this->assertInstanceOf(AccessTokenEntityInterface::class, $response->getAccessToken());
         $this->assertInstanceOf(RefreshTokenEntityInterface::class, $response->getRefreshToken());
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
-     * @expectedExceptionCode 3
-     */
     public function testRespondToAccessTokenRequestMissingRedirectUri()
     {
         $client = new ClientEntity();
         $client->setIdentifier('foo');
+        $client->setConfidential();
         $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
         $clientRepositoryMock->method('getClientEntity')->willReturn($client);
 
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setEncryptionKey($this->cryptStub->getKey());
@@ -897,24 +914,24 @@ class AuthCodeGrantTest extends TestCase
             ]
         );
 
-        $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
+        $this->expectExceptionCode(3);
+
+        $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
-     * @expectedExceptionCode 3
-     */
     public function testRespondToAccessTokenRequestRedirectUriMismatch()
     {
         $client = new ClientEntity();
         $client->setIdentifier('foo');
+        $client->setConfidential();
         $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
         $clientRepositoryMock->method('getClientEntity')->willReturn($client);
 
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setEncryptionKey($this->cryptStub->getKey());
@@ -945,17 +962,17 @@ class AuthCodeGrantTest extends TestCase
             ]
         );
 
-        $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
+        $this->expectExceptionCode(3);
+
+        $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
-     * @expectedExceptionCode 3
-     */
     public function testRespondToAccessTokenRequestMissingCode()
     {
         $client = new ClientEntity();
         $client->setRedirectUri('http://foo/bar');
+        $client->setConfidential();
         $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
         $clientRepositoryMock->method('getClientEntity')->willReturn($client);
 
@@ -965,7 +982,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setAccessTokenRepository($accessTokenRepositoryMock);
@@ -989,32 +1006,25 @@ class AuthCodeGrantTest extends TestCase
             ]
         );
 
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
+        $this->expectExceptionCode(3);
+
         /* @var StubResponseType $response */
-        $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+        $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
     }
 
     public function testRespondToAccessTokenRequestExpiredCode()
     {
-        $client = new ClientEntity();
-        $client->setIdentifier('foo');
-        $client->setRedirectUri('http://foo/bar');
         $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
-        $clientRepositoryMock->method('getClientEntity')->willReturn($client);
-
-        $accessTokenRepositoryMock = $this->getMockBuilder(AccessTokenRepositoryInterface::class)->getMock();
-        $accessTokenRepositoryMock->method('persistNewAccessToken')->willReturnSelf();
-
-        $refreshTokenRepositoryMock = $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock();
-        $refreshTokenRepositoryMock->method('persistNewRefreshToken')->willReturnSelf();
+        $clientRepositoryMock->method('getClientEntity')->willReturn(new ClientEntity());
 
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
+
         $grant->setClientRepository($clientRepositoryMock);
-        $grant->setAccessTokenRepository($accessTokenRepositoryMock);
-        $grant->setRefreshTokenRepository($refreshTokenRepositoryMock);
         $grant->setEncryptionKey($this->cryptStub->getKey());
 
         $request = new ServerRequest(
@@ -1047,7 +1057,7 @@ class AuthCodeGrantTest extends TestCase
 
         try {
             /* @var StubResponseType $response */
-            $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+            $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
         } catch (OAuthServerException $e) {
             $this->assertEquals($e->getHint(), 'Authorization code has expired');
         }
@@ -1058,6 +1068,7 @@ class AuthCodeGrantTest extends TestCase
         $client = new ClientEntity();
         $client->setIdentifier('foo');
         $client->setRedirectUri('http://foo/bar');
+        $client->setConfidential();
         $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
         $clientRepositoryMock->method('getClientEntity')->willReturn($client);
 
@@ -1073,7 +1084,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $authCodeRepositoryMock,
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setAccessTokenRepository($accessTokenRepositoryMock);
@@ -1110,7 +1121,7 @@ class AuthCodeGrantTest extends TestCase
 
         try {
             /* @var StubResponseType $response */
-            $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+            $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
         } catch (OAuthServerException $e) {
             $this->assertEquals($e->getHint(), 'Authorization code has been revoked');
         }
@@ -1121,6 +1132,7 @@ class AuthCodeGrantTest extends TestCase
         $client = new ClientEntity();
         $client->setIdentifier('foo');
         $client->setRedirectUri('http://foo/bar');
+        $client->setConfidential();
         $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
         $clientRepositoryMock->method('getClientEntity')->willReturn($client);
 
@@ -1133,7 +1145,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setAccessTokenRepository($accessTokenRepositoryMock);
@@ -1170,7 +1182,7 @@ class AuthCodeGrantTest extends TestCase
 
         try {
             /* @var StubResponseType $response */
-            $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+            $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
         } catch (OAuthServerException $e) {
             $this->assertEquals($e->getHint(), 'Authorization code was not issued to this client');
         }
@@ -1181,6 +1193,7 @@ class AuthCodeGrantTest extends TestCase
         $client = new ClientEntity();
         $client->setIdentifier('foo');
         $client->setRedirectUri('http://foo/bar');
+        $client->setConfidential();
         $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
         $clientRepositoryMock->method('getClientEntity')->willReturn($client);
 
@@ -1193,7 +1206,7 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setAccessTokenRepository($accessTokenRepositoryMock);
@@ -1219,7 +1232,7 @@ class AuthCodeGrantTest extends TestCase
 
         try {
             /* @var StubResponseType $response */
-            $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+            $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
         } catch (OAuthServerException $e) {
             $this->assertEquals($e->getHint(), 'Cannot decrypt the authorization code');
         }
@@ -1230,6 +1243,7 @@ class AuthCodeGrantTest extends TestCase
         $client = new ClientEntity();
         $client->setIdentifier('foo');
         $client->setRedirectUri('http://foo/bar');
+        $client->setConfidential();
         $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
         $clientRepositoryMock->method('getClientEntity')->willReturn($client);
 
@@ -1249,9 +1263,9 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
-        $grant->enableCodeExchangeProof();
+
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setAccessTokenRepository($accessTokenRepositoryMock);
         $grant->setRefreshTokenRepository($refreshTokenRepositoryMock);
@@ -1291,7 +1305,7 @@ class AuthCodeGrantTest extends TestCase
 
         try {
             /* @var StubResponseType $response */
-            $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+            $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
         } catch (OAuthServerException $e) {
             $this->assertEquals($e->getHint(), 'Failed to verify `code_verifier`.');
         }
@@ -1302,6 +1316,7 @@ class AuthCodeGrantTest extends TestCase
         $client = new ClientEntity();
         $client->setIdentifier('foo');
         $client->setRedirectUri('http://foo/bar');
+        $client->setConfidential();
         $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
         $clientRepositoryMock->method('getClientEntity')->willReturn($client);
 
@@ -1321,9 +1336,9 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
-        $grant->enableCodeExchangeProof();
+
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setAccessTokenRepository($accessTokenRepositoryMock);
         $grant->setRefreshTokenRepository($refreshTokenRepositoryMock);
@@ -1363,7 +1378,7 @@ class AuthCodeGrantTest extends TestCase
 
         try {
             /* @var StubResponseType $response */
-            $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+            $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
         } catch (OAuthServerException $e) {
             $this->assertEquals($e->getHint(), 'Code Verifier must follow the specifications of RFC-7636.');
         }
@@ -1374,6 +1389,7 @@ class AuthCodeGrantTest extends TestCase
         $client = new ClientEntity();
         $client->setIdentifier('foo');
         $client->setRedirectUri('http://foo/bar');
+        $client->setConfidential();
         $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
         $clientRepositoryMock->method('getClientEntity')->willReturn($client);
 
@@ -1393,9 +1409,9 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
-        $grant->enableCodeExchangeProof();
+
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setAccessTokenRepository($accessTokenRepositoryMock);
         $grant->setRefreshTokenRepository($refreshTokenRepositoryMock);
@@ -1435,7 +1451,7 @@ class AuthCodeGrantTest extends TestCase
 
         try {
             /* @var StubResponseType $response */
-            $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+            $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
         } catch (OAuthServerException $e) {
             $this->assertEquals($e->getHint(), 'Code Verifier must follow the specifications of RFC-7636.');
         }
@@ -1446,6 +1462,7 @@ class AuthCodeGrantTest extends TestCase
         $client = new ClientEntity();
         $client->setIdentifier('foo');
         $client->setRedirectUri('http://foo/bar');
+        $client->setConfidential();
         $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
         $clientRepositoryMock->method('getClientEntity')->willReturn($client);
 
@@ -1465,9 +1482,9 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
-        $grant->enableCodeExchangeProof();
+
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setAccessTokenRepository($accessTokenRepositoryMock);
         $grant->setRefreshTokenRepository($refreshTokenRepositoryMock);
@@ -1507,7 +1524,7 @@ class AuthCodeGrantTest extends TestCase
 
         try {
             /* @var StubResponseType $response */
-            $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+            $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
         } catch (OAuthServerException $e) {
             $this->assertEquals($e->getHint(), 'Code Verifier must follow the specifications of RFC-7636.');
         }
@@ -1518,6 +1535,7 @@ class AuthCodeGrantTest extends TestCase
         $client = new ClientEntity();
         $client->setIdentifier('foo');
         $client->setRedirectUri('http://foo/bar');
+        $client->setConfidential();
         $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
         $clientRepositoryMock->method('getClientEntity')->willReturn($client);
 
@@ -1537,9 +1555,9 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
-        $grant->enableCodeExchangeProof();
+
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setAccessTokenRepository($accessTokenRepositoryMock);
         $grant->setRefreshTokenRepository($refreshTokenRepositoryMock);
@@ -1578,7 +1596,7 @@ class AuthCodeGrantTest extends TestCase
 
         try {
             /* @var StubResponseType $response */
-            $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+            $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
         } catch (OAuthServerException $e) {
             $this->assertEquals($e->getHint(), 'Check the `code_verifier` parameter');
         }
@@ -1601,17 +1619,14 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $authCodeRepository,
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setEncryptionKey($this->cryptStub->getKey());
+        $grant->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
 
         $this->assertInstanceOf(RedirectResponse::class, $grant->completeAuthorizationRequest($authRequest));
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
-     * @expectedExceptionCode 7
-     */
     public function testAuthCodeRepositoryFailToPersist()
     {
         $authRequest = new AuthorizationRequest();
@@ -1627,17 +1642,16 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $authCodeRepository,
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setEncryptionKey($this->cryptStub->getKey());
 
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
+        $this->expectExceptionCode(7);
+
         $this->assertInstanceOf(RedirectResponse::class, $grant->completeAuthorizationRequest($authRequest));
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\UniqueTokenIdentifierConstraintViolationException
-     * @expectedExceptionCode 100
-     */
     public function testAuthCodeRepositoryFailToPersistUniqueNoInfiniteLoop()
     {
         $authRequest = new AuthorizationRequest();
@@ -1653,9 +1667,12 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $authCodeRepository,
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
 
+        $this->expectException(\League\OAuth2\Server\Exception\UniqueTokenIdentifierConstraintViolationException::class);
+        $this->expectExceptionCode(100);
+
         $this->assertInstanceOf(RedirectResponse::class, $grant->completeAuthorizationRequest($authRequest));
     }
 
@@ -1684,13 +1701,14 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setScopeRepository($scopeRepositoryMock);
         $grant->setAccessTokenRepository($accessTokenRepositoryMock);
         $grant->setRefreshTokenRepository($refreshTokenRepositoryMock);
         $grant->setEncryptionKey($this->cryptStub->getKey());
+        $grant->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
 
         $request = new ServerRequest(
             [],
@@ -1721,16 +1739,12 @@ class AuthCodeGrantTest extends TestCase
         );
 
         /** @var StubResponseType $response */
-        $response = $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+        $response = $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
 
         $this->assertInstanceOf(AccessTokenEntityInterface::class, $response->getAccessToken());
         $this->assertInstanceOf(RefreshTokenEntityInterface::class, $response->getRefreshToken());
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
-     * @expectedExceptionCode 7
-     */
     public function testRefreshTokenRepositoryFailToPersist()
     {
         $client = new ClientEntity();
@@ -1755,13 +1769,14 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setScopeRepository($scopeRepositoryMock);
         $grant->setAccessTokenRepository($accessTokenRepositoryMock);
         $grant->setRefreshTokenRepository($refreshTokenRepositoryMock);
         $grant->setEncryptionKey($this->cryptStub->getKey());
+        $grant->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
 
         $request = new ServerRequest(
             [],
@@ -1791,17 +1806,16 @@ class AuthCodeGrantTest extends TestCase
             ]
         );
 
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
+        $this->expectExceptionCode(7);
+
         /** @var StubResponseType $response */
-        $response = $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+        $response = $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
 
         $this->assertInstanceOf(AccessTokenEntityInterface::class, $response->getAccessToken());
         $this->assertInstanceOf(RefreshTokenEntityInterface::class, $response->getRefreshToken());
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\UniqueTokenIdentifierConstraintViolationException
-     * @expectedExceptionCode 100
-     */
     public function testRefreshTokenRepositoryFailToPersistUniqueNoInfiniteLoop()
     {
         $client = new ClientEntity();
@@ -1826,13 +1840,14 @@ class AuthCodeGrantTest extends TestCase
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setScopeRepository($scopeRepositoryMock);
         $grant->setAccessTokenRepository($accessTokenRepositoryMock);
         $grant->setRefreshTokenRepository($refreshTokenRepositoryMock);
         $grant->setEncryptionKey($this->cryptStub->getKey());
+        $grant->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
 
         $request = new ServerRequest(
             [],
@@ -1862,24 +1877,60 @@ class AuthCodeGrantTest extends TestCase
             ]
         );
 
+        $this->expectException(\League\OAuth2\Server\Exception\UniqueTokenIdentifierConstraintViolationException::class);
+        $this->expectExceptionCode(100);
+
         /** @var StubResponseType $response */
-        $response = $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+        $response = $grant->respondToAccessTokenRequest($request, new StubResponseType(), new DateInterval('PT10M'));
 
         $this->assertInstanceOf(AccessTokenEntityInterface::class, $response->getAccessToken());
         $this->assertInstanceOf(RefreshTokenEntityInterface::class, $response->getRefreshToken());
     }
 
-    /**
-     * @expectedException \LogicException
-     */
     public function testCompleteAuthorizationRequestNoUser()
     {
         $grant = new AuthCodeGrant(
             $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
             $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
 
+        $this->expectException(\LogicException::class);
+
         $grant->completeAuthorizationRequest(new AuthorizationRequest());
     }
+
+    public function testPublicClientAuthCodeRequestRejectedWhenCodeChallengeRequiredButNotGiven()
+    {
+        $client = new ClientEntity();
+        $client->setRedirectUri('http://foo/bar');
+
+        $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
+        $clientRepositoryMock->method('getClientEntity')->willReturn($client);
+
+        $scope = new ScopeEntity();
+        $scopeRepositoryMock = $this->getMockBuilder(ScopeRepositoryInterface::class)->getMock();
+        $scopeRepositoryMock->method('getScopeEntityByIdentifier')->willReturn($scope);
+
+        $grant = new AuthCodeGrant(
+            $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock(),
+            $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock(),
+            new DateInterval('PT10M')
+        );
+
+        $grant->setClientRepository($clientRepositoryMock);
+        $grant->setScopeRepository($scopeRepositoryMock);
+        $grant->setDefaultScope(self::DEFAULT_SCOPE);
+
+        $request = (new ServerRequest())->withQueryParams([
+            'response_type' => 'code',
+            'client_id'     => 'foo',
+            'redirect_uri'  => 'http://foo/bar',
+        ]);
+
+        $this->expectException(OAuthServerException::class);
+        $this->expectExceptionCode(3);
+
+        $grant->validateAuthorizationRequest($request);
+    }
 }
diff --git a/tests/Grant/ClientCredentialsGrantTest.php b/tests/Grant/ClientCredentialsGrantTest.php
index 6c7b5a36..54be52fd 100644
--- a/tests/Grant/ClientCredentialsGrantTest.php
+++ b/tests/Grant/ClientCredentialsGrantTest.php
@@ -2,6 +2,8 @@
 
 namespace LeagueTests\Grant;
 
+use DateInterval;
+use League\OAuth2\Server\CryptKey;
 use League\OAuth2\Server\Entities\AccessTokenEntityInterface;
 use League\OAuth2\Server\Grant\ClientCredentialsGrant;
 use League\OAuth2\Server\Repositories\AccessTokenRepositoryInterface;
@@ -44,17 +46,15 @@ class ClientCredentialsGrantTest extends TestCase
         $grant->setAccessTokenRepository($accessTokenRepositoryMock);
         $grant->setScopeRepository($scopeRepositoryMock);
         $grant->setDefaultScope(self::DEFAULT_SCOPE);
+        $grant->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
 
-        $serverRequest = new ServerRequest();
-        $serverRequest = $serverRequest->withParsedBody(
-            [
-                'client_id'     => 'foo',
-                'client_secret' => 'bar',
-            ]
-        );
+        $serverRequest = (new ServerRequest())->withParsedBody([
+            'client_id'     => 'foo',
+            'client_secret' => 'bar',
+        ]);
 
         $responseType = new StubResponseType();
-        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new \DateInterval('PT5M'));
+        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new DateInterval('PT5M'));
 
         $this->assertInstanceOf(AccessTokenEntityInterface::class, $responseType->getAccessToken());
     }
diff --git a/tests/Grant/ImplicitGrantTest.php b/tests/Grant/ImplicitGrantTest.php
index 8cfcfff5..e9523669 100644
--- a/tests/Grant/ImplicitGrantTest.php
+++ b/tests/Grant/ImplicitGrantTest.php
@@ -2,6 +2,7 @@
 
 namespace LeagueTests\Grant;
 
+use DateInterval;
 use League\OAuth2\Server\CryptKey;
 use League\OAuth2\Server\Exception\OAuthServerException;
 use League\OAuth2\Server\Exception\UniqueTokenIdentifierConstraintViolationException;
@@ -30,56 +31,47 @@ class ImplicitGrantTest extends TestCase
      */
     protected $cryptStub;
 
-    public function setUp()
+    public function setUp(): void
     {
         $this->cryptStub = new CryptTraitStub();
     }
 
     public function testGetIdentifier()
     {
-        $grant = new ImplicitGrant(new \DateInterval('PT10M'));
+        $grant = new ImplicitGrant(new DateInterval('PT10M'));
         $this->assertEquals('implicit', $grant->getIdentifier());
     }
 
     public function testCanRespondToAccessTokenRequest()
     {
-        $grant = new ImplicitGrant(new \DateInterval('PT10M'));
+        $grant = new ImplicitGrant(new DateInterval('PT10M'));
 
         $this->assertFalse(
             $grant->canRespondToAccessTokenRequest(new ServerRequest())
         );
     }
 
-    /**
-     * @expectedException \LogicException
-     */
     public function testRespondToAccessTokenRequest()
     {
-        $grant = new ImplicitGrant(new \DateInterval('PT10M'));
+        $grant = new ImplicitGrant(new DateInterval('PT10M'));
+
+        $this->expectException(\LogicException::class);
+
         $grant->respondToAccessTokenRequest(
             new ServerRequest(),
             new StubResponseType(),
-            new \DateInterval('PT10M')
+            new DateInterval('PT10M')
         );
     }
 
     public function testCanRespondToAuthorizationRequest()
     {
-        $grant = new ImplicitGrant(new \DateInterval('PT10M'));
+        $grant = new ImplicitGrant(new DateInterval('PT10M'));
 
-        $request = new ServerRequest(
-            [],
-            [],
-            null,
-            null,
-            'php://input',
-            $headers = [],
-            $cookies = [],
-            $queryParams = [
-                'response_type' => 'token',
-                'client_id'     => 'foo',
-            ]
-        );
+        $request = (new ServerRequest())->withQueryParams([
+            'response_type' => 'token',
+            'client_id'     => 'foo',
+        ]);
 
         $this->assertTrue($grant->canRespondToAuthorizationRequest($request));
     }
@@ -95,25 +87,16 @@ class ImplicitGrantTest extends TestCase
         $scopeEntity = new ScopeEntity();
         $scopeRepositoryMock->method('getScopeEntityByIdentifier')->willReturn($scopeEntity);
 
-        $grant = new ImplicitGrant(new \DateInterval('PT10M'));
+        $grant = new ImplicitGrant(new DateInterval('PT10M'));
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setScopeRepository($scopeRepositoryMock);
         $grant->setDefaultScope(self::DEFAULT_SCOPE);
 
-        $request = new ServerRequest(
-            [],
-            [],
-            null,
-            null,
-            'php://input',
-            $headers = [],
-            $cookies = [],
-            $queryParams = [
-                'response_type' => 'code',
-                'client_id'     => 'foo',
-                'redirect_uri'  => 'http://foo/bar',
-            ]
-        );
+        $request = (new ServerRequest())->withQueryParams([
+            'response_type' => 'code',
+            'client_id'     => 'foo',
+            'redirect_uri'  => 'http://foo/bar',
+        ]);
 
         $this->assertInstanceOf(AuthorizationRequest::class, $grant->validateAuthorizationRequest($request));
     }
@@ -129,89 +112,54 @@ class ImplicitGrantTest extends TestCase
         $scopeEntity = new ScopeEntity();
         $scopeRepositoryMock->method('getScopeEntityByIdentifier')->willReturn($scopeEntity);
 
-        $grant = new ImplicitGrant(new \DateInterval('PT10M'));
+        $grant = new ImplicitGrant(new DateInterval('PT10M'));
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setScopeRepository($scopeRepositoryMock);
         $grant->setDefaultScope(self::DEFAULT_SCOPE);
 
-        $request = new ServerRequest(
-            [],
-            [],
-            null,
-            null,
-            'php://input',
-            $headers = [],
-            $cookies = [],
-            $queryParams = [
-                'response_type' => 'code',
-                'client_id'     => 'foo',
-                'redirect_uri'  => 'http://foo/bar',
-            ]
-        );
+        $request = (new ServerRequest())->withQueryParams([
+            'response_type' => 'code',
+            'client_id' => 'foo',
+            'redirect_uri' => 'http://foo/bar',
+        ]);
 
         $this->assertInstanceOf(AuthorizationRequest::class, $grant->validateAuthorizationRequest($request));
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
-     * @expectedExceptionCode 3
-     */
     public function testValidateAuthorizationRequestMissingClientId()
     {
         $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
 
-        $grant = new ImplicitGrant(new \DateInterval('PT10M'));
+        $grant = new ImplicitGrant(new DateInterval('PT10M'));
         $grant->setClientRepository($clientRepositoryMock);
 
-        $request = new ServerRequest(
-            [],
-            [],
-            null,
-            null,
-            'php://input',
-            $headers = [],
-            $cookies = [],
-            $queryParams = [
-                'response_type' => 'code',
-            ]
-        );
+        $request = (new ServerRequest())->withQueryParams(['response_type' => 'code']);
+
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
+        $this->expectExceptionCode(3);
 
         $grant->validateAuthorizationRequest($request);
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
-     * @expectedExceptionCode 4
-     */
     public function testValidateAuthorizationRequestInvalidClientId()
     {
         $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
         $clientRepositoryMock->method('getClientEntity')->willReturn(null);
 
-        $grant = new ImplicitGrant(new \DateInterval('PT10M'));
+        $grant = new ImplicitGrant(new DateInterval('PT10M'));
         $grant->setClientRepository($clientRepositoryMock);
 
-        $request = new ServerRequest(
-            [],
-            [],
-            null,
-            null,
-            'php://input',
-            $headers = [],
-            $cookies = [],
-            $queryParams = [
-                'response_type' => 'code',
-                'client_id'     => 'foo',
-            ]
-        );
+        $request = (new ServerRequest())->withQueryParams([
+            'response_type' => 'code',
+            'client_id'     => 'foo',
+        ]);
+
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
+        $this->expectExceptionCode(4);
 
         $grant->validateAuthorizationRequest($request);
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
-     * @expectedExceptionCode 4
-     */
     public function testValidateAuthorizationRequestBadRedirectUriString()
     {
         $client = new ClientEntity();
@@ -219,31 +167,21 @@ class ImplicitGrantTest extends TestCase
         $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
         $clientRepositoryMock->method('getClientEntity')->willReturn($client);
 
-        $grant = new ImplicitGrant(new \DateInterval('PT10M'));
+        $grant = new ImplicitGrant(new DateInterval('PT10M'));
         $grant->setClientRepository($clientRepositoryMock);
 
-        $request = new ServerRequest(
-            [],
-            [],
-            null,
-            null,
-            'php://input',
-            $headers = [],
-            $cookies = [],
-            $queryParams = [
-                'response_type' => 'code',
-                'client_id'     => 'foo',
-                'redirect_uri'  => 'http://bar',
-            ]
-        );
+        $request = (new ServerRequest())->withQueryParams([
+            'response_type' => 'code',
+            'client_id' => 'foo',
+            'redirect_uri' => 'http://bar',
+        ]);
+
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
+        $this->expectExceptionCode(4);
 
         $grant->validateAuthorizationRequest($request);
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
-     * @expectedExceptionCode 4
-     */
     public function testValidateAuthorizationRequestBadRedirectUriArray()
     {
         $client = new ClientEntity();
@@ -251,37 +189,37 @@ class ImplicitGrantTest extends TestCase
         $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
         $clientRepositoryMock->method('getClientEntity')->willReturn($client);
 
-        $grant = new ImplicitGrant(new \DateInterval('PT10M'));
+        $grant = new ImplicitGrant(new DateInterval('PT10M'));
         $grant->setClientRepository($clientRepositoryMock);
 
-        $request = new ServerRequest(
-            [],
-            [],
-            null,
-            null,
-            'php://input',
-            $headers = [],
-            $cookies = [],
-            $queryParams = [
-                'response_type' => 'code',
-                'client_id'     => 'foo',
-                'redirect_uri'  => 'http://bar',
-            ]
-        );
+        $request = (new ServerRequest())->withQueryParams([
+            'response_type' => 'code',
+            'client_id'     => 'foo',
+            'redirect_uri'  => 'http://bar',
+        ]);
+
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
+        $this->expectExceptionCode(4);
 
         $grant->validateAuthorizationRequest($request);
     }
 
     public function testCompleteAuthorizationRequest()
     {
+        $client = new ClientEntity();
+        $client->setIdentifier('identifier');
+
         $authRequest = new AuthorizationRequest();
         $authRequest->setAuthorizationApproved(true);
-        $authRequest->setClient(new ClientEntity());
+        $authRequest->setClient($client);
         $authRequest->setGrantTypeId('authorization_code');
         $authRequest->setUser(new UserEntity());
 
+        $accessToken = new AccessTokenEntity();
+        $accessToken->setClient($client);
+
         $accessTokenRepositoryMock = $this->getMockBuilder(AccessTokenRepositoryInterface::class)->getMock();
-        $accessTokenRepositoryMock->method('getNewToken')->willReturn(new AccessTokenEntity());
+        $accessTokenRepositoryMock->method('getNewToken')->willReturn($accessToken);
         $accessTokenRepositoryMock->method('persistNewAccessToken')->willReturnSelf();
 
         $scopeRepositoryMock = $this->getMockBuilder(ScopeRepositoryInterface::class)->getMock();
@@ -295,10 +233,6 @@ class ImplicitGrantTest extends TestCase
         $this->assertInstanceOf(RedirectResponse::class, $grant->completeAuthorizationRequest($authRequest));
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
-     * @expectedExceptionCode 9
-     */
     public function testCompleteAuthorizationRequestDenied()
     {
         $authRequest = new AuthorizationRequest();
@@ -319,20 +253,29 @@ class ImplicitGrantTest extends TestCase
         $grant->setAccessTokenRepository($accessTokenRepositoryMock);
         $grant->setScopeRepository($scopeRepositoryMock);
 
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
+        $this->expectExceptionCode(9);
+
         $grant->completeAuthorizationRequest($authRequest);
     }
 
     public function testAccessTokenRepositoryUniqueConstraintCheck()
     {
+        $client = new ClientEntity();
+        $client->setIdentifier('identifier');
+
         $authRequest = new AuthorizationRequest();
         $authRequest->setAuthorizationApproved(true);
-        $authRequest->setClient(new ClientEntity());
+        $authRequest->setClient($client);
         $authRequest->setGrantTypeId('authorization_code');
         $authRequest->setUser(new UserEntity());
 
-        /** @var AccessTokenRepositoryInterface|\PHPUnit_Framework_MockObject_MockObject $accessTokenRepositoryMock */
+        $accessToken = new AccessTokenEntity();
+        $accessToken->setClient($client);
+
+        /** @var AccessTokenRepositoryInterface|\PHPUnit\Framework\MockObject\MockObject $accessTokenRepositoryMock */
         $accessTokenRepositoryMock = $this->getMockBuilder(AccessTokenRepositoryInterface::class)->getMock();
-        $accessTokenRepositoryMock->method('getNewToken')->willReturn(new AccessTokenEntity());
+        $accessTokenRepositoryMock->method('getNewToken')->willReturn($accessToken);
         $accessTokenRepositoryMock->expects($this->at(0))->method('persistNewAccessToken')->willThrowException(UniqueTokenIdentifierConstraintViolationException::create());
         $accessTokenRepositoryMock->expects($this->at(1))->method('persistNewAccessToken')->willReturnSelf();
 
@@ -347,10 +290,6 @@ class ImplicitGrantTest extends TestCase
         $this->assertInstanceOf(RedirectResponse::class, $grant->completeAuthorizationRequest($authRequest));
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
-     * @expectedExceptionCode 7
-     */
     public function testAccessTokenRepositoryFailToPersist()
     {
         $authRequest = new AuthorizationRequest();
@@ -359,7 +298,7 @@ class ImplicitGrantTest extends TestCase
         $authRequest->setGrantTypeId('authorization_code');
         $authRequest->setUser(new UserEntity());
 
-        /** @var AccessTokenRepositoryInterface|\PHPUnit_Framework_MockObject_MockObject $accessTokenRepositoryMock */
+        /** @var AccessTokenRepositoryInterface|\PHPUnit\Framework\MockObject\MockObject $accessTokenRepositoryMock */
         $accessTokenRepositoryMock = $this->getMockBuilder(AccessTokenRepositoryInterface::class)->getMock();
         $accessTokenRepositoryMock->method('getNewToken')->willReturn(new AccessTokenEntity());
         $accessTokenRepositoryMock->method('persistNewAccessToken')->willThrowException(OAuthServerException::serverError('something bad happened'));
@@ -372,13 +311,12 @@ class ImplicitGrantTest extends TestCase
         $grant->setAccessTokenRepository($accessTokenRepositoryMock);
         $grant->setScopeRepository($scopeRepositoryMock);
 
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
+        $this->expectExceptionCode(7);
+
         $grant->completeAuthorizationRequest($authRequest);
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\UniqueTokenIdentifierConstraintViolationException
-     * @expectedExceptionCode 100
-     */
     public function testAccessTokenRepositoryFailToPersistUniqueNoInfiniteLoop()
     {
         $authRequest = new AuthorizationRequest();
@@ -387,7 +325,7 @@ class ImplicitGrantTest extends TestCase
         $authRequest->setGrantTypeId('authorization_code');
         $authRequest->setUser(new UserEntity());
 
-        /** @var AccessTokenRepositoryInterface|\PHPUnit_Framework_MockObject_MockObject $accessTokenRepositoryMock */
+        /** @var AccessTokenRepositoryInterface|\PHPUnit\Framework\MockObject\MockObject $accessTokenRepositoryMock */
         $accessTokenRepositoryMock = $this->getMockBuilder(AccessTokenRepositoryInterface::class)->getMock();
         $accessTokenRepositoryMock->method('getNewToken')->willReturn(new AccessTokenEntity());
         $accessTokenRepositoryMock->method('persistNewAccessToken')->willThrowException(UniqueTokenIdentifierConstraintViolationException::create());
@@ -400,34 +338,38 @@ class ImplicitGrantTest extends TestCase
         $grant->setAccessTokenRepository($accessTokenRepositoryMock);
         $grant->setScopeRepository($scopeRepositoryMock);
 
+        $this->expectException(\League\OAuth2\Server\Exception\UniqueTokenIdentifierConstraintViolationException::class);
+        $this->expectExceptionCode(100);
+
         $grant->completeAuthorizationRequest($authRequest);
     }
 
-    /**
-     * @expectedException \LogicException
-     */
     public function testSetRefreshTokenTTL()
     {
-        $grant = new ImplicitGrant(new \DateInterval('PT10M'));
-        $grant->setRefreshTokenTTL(new \DateInterval('PT10M'));
+        $grant = new ImplicitGrant(new DateInterval('PT10M'));
+
+        $this->expectException(\LogicException::class);
+
+        $grant->setRefreshTokenTTL(new DateInterval('PT10M'));
     }
 
-    /**
-     * @expectedException \LogicException
-     */
     public function testSetRefreshTokenRepository()
     {
-        $grant = new ImplicitGrant(new \DateInterval('PT10M'));
+        $grant = new ImplicitGrant(new DateInterval('PT10M'));
+
         $refreshTokenRepositoryMock = $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock();
+
+        $this->expectException(\LogicException::class);
+
         $grant->setRefreshTokenRepository($refreshTokenRepositoryMock);
     }
 
-    /**
-     * @expectedException \LogicException
-     */
     public function testCompleteAuthorizationRequestNoUser()
     {
-        $grant = new ImplicitGrant(new \DateInterval('PT10M'));
+        $grant = new ImplicitGrant(new DateInterval('PT10M'));
+
+        $this->expectException(\LogicException::class);
+
         $grant->completeAuthorizationRequest(new AuthorizationRequest());
     }
 }
diff --git a/tests/Grant/PasswordGrantTest.php b/tests/Grant/PasswordGrantTest.php
index 28183a98..6568d06a 100644
--- a/tests/Grant/PasswordGrantTest.php
+++ b/tests/Grant/PasswordGrantTest.php
@@ -2,6 +2,8 @@
 
 namespace LeagueTests\Grant;
 
+use DateInterval;
+use League\OAuth2\Server\CryptKey;
 use League\OAuth2\Server\Entities\AccessTokenEntityInterface;
 use League\OAuth2\Server\Entities\RefreshTokenEntityInterface;
 use League\OAuth2\Server\Grant\PasswordGrant;
@@ -60,19 +62,17 @@ class PasswordGrantTest extends TestCase
         $grant->setAccessTokenRepository($accessTokenRepositoryMock);
         $grant->setScopeRepository($scopeRepositoryMock);
         $grant->setDefaultScope(self::DEFAULT_SCOPE);
+        $grant->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
 
-        $serverRequest = new ServerRequest();
-        $serverRequest = $serverRequest->withParsedBody(
-            [
-                'client_id'     => 'foo',
-                'client_secret' => 'bar',
-                'username'      => 'foo',
-                'password'      => 'bar',
-            ]
-        );
+        $serverRequest = (new ServerRequest())->withParsedBody([
+            'client_id'     => 'foo',
+            'client_secret' => 'bar',
+            'username'      => 'foo',
+            'password'      => 'bar',
+        ]);
 
         $responseType = new StubResponseType();
-        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new \DateInterval('PT5M'));
+        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new DateInterval('PT5M'));
 
         $this->assertInstanceOf(AccessTokenEntityInterface::class, $responseType->getAccessToken());
         $this->assertInstanceOf(RefreshTokenEntityInterface::class, $responseType->getRefreshToken());
@@ -105,16 +105,14 @@ class PasswordGrantTest extends TestCase
         $grant->setAccessTokenRepository($accessTokenRepositoryMock);
         $grant->setScopeRepository($scopeRepositoryMock);
         $grant->setDefaultScope(self::DEFAULT_SCOPE);
+        $grant->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
 
-        $serverRequest = new ServerRequest();
-        $serverRequest = $serverRequest->withParsedBody(
-            [
-                'client_id'     => 'foo',
-                'client_secret' => 'bar',
-                'username'      => 'foo',
-                'password'      => 'bar',
-            ]
-        );
+        $serverRequest = (new ServerRequest())->withParsedBody([
+            'client_id'     => 'foo',
+            'client_secret' => 'bar',
+            'username'      => 'foo',
+            'password'      => 'bar',
+        ]);
 
         $responseType = new StubResponseType();
         $grant->respondToAccessTokenRequest($serverRequest, $responseType, new \DateInterval('PT5M'));
@@ -123,9 +121,6 @@ class PasswordGrantTest extends TestCase
         $this->assertNull($responseType->getRefreshToken());
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
-     */
     public function testRespondToRequestMissingUsername()
     {
         $client = new ClientEntity();
@@ -142,21 +137,18 @@ class PasswordGrantTest extends TestCase
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setAccessTokenRepository($accessTokenRepositoryMock);
 
-        $serverRequest = new ServerRequest();
-        $serverRequest = $serverRequest->withParsedBody(
-            [
-                'client_id'     => 'foo',
-                'client_secret' => 'bar',
-            ]
-        );
+        $serverRequest = (new ServerRequest())->withQueryParams([
+            'client_id'     => 'foo',
+            'client_secret' => 'bar',
+        ]);
 
         $responseType = new StubResponseType();
-        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new \DateInterval('PT5M'));
+
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
+
+        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new DateInterval('PT5M'));
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
-     */
     public function testRespondToRequestMissingPassword()
     {
         $client = new ClientEntity();
@@ -173,22 +165,19 @@ class PasswordGrantTest extends TestCase
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setAccessTokenRepository($accessTokenRepositoryMock);
 
-        $serverRequest = new ServerRequest();
-        $serverRequest = $serverRequest->withParsedBody(
-            [
-                'client_id'     => 'foo',
-                'client_secret' => 'bar',
-                'username'      => 'alex',
-            ]
-        );
+        $serverRequest = (new ServerRequest())->withParsedBody([
+            'client_id'     => 'foo',
+            'client_secret' => 'bar',
+            'username'      => 'alex',
+        ]);
 
         $responseType = new StubResponseType();
-        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new \DateInterval('PT5M'));
+
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
+
+        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new DateInterval('PT5M'));
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
-     */
     public function testRespondToRequestBadCredentials()
     {
         $client = new ClientEntity();
@@ -206,17 +195,18 @@ class PasswordGrantTest extends TestCase
         $grant->setClientRepository($clientRepositoryMock);
         $grant->setAccessTokenRepository($accessTokenRepositoryMock);
 
-        $serverRequest = new ServerRequest();
-        $serverRequest = $serverRequest->withParsedBody(
-            [
-                'client_id'     => 'foo',
-                'client_secret' => 'bar',
-                'username'      => 'alex',
-                'password'      => 'whisky',
-            ]
-        );
+        $serverRequest = (new ServerRequest())->withParsedBody([
+            'client_id' => 'foo',
+            'client_secret' => 'bar',
+            'username' => 'alex',
+            'password' => 'whisky',
+        ]);
 
         $responseType = new StubResponseType();
-        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new \DateInterval('PT5M'));
+
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
+        $this->expectExceptionCode(10);
+
+        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new DateInterval('PT5M'));
     }
 }
diff --git a/tests/Grant/RefreshTokenGrantTest.php b/tests/Grant/RefreshTokenGrantTest.php
index 8f205361..21a5eeb8 100644
--- a/tests/Grant/RefreshTokenGrantTest.php
+++ b/tests/Grant/RefreshTokenGrantTest.php
@@ -2,6 +2,7 @@
 
 namespace LeagueTests\Grant;
 
+use DateInterval;
 use League\OAuth2\Server\CryptKey;
 use League\OAuth2\Server\Entities\AccessTokenEntityInterface;
 use League\OAuth2\Server\Entities\RefreshTokenEntityInterface;
@@ -26,7 +27,7 @@ class RefreshTokenGrantTest extends TestCase
      */
     protected $cryptStub;
 
-    public function setUp()
+    public function setUp(): void
     {
         $this->cryptStub = new CryptTraitStub();
     }
@@ -79,8 +80,7 @@ class RefreshTokenGrantTest extends TestCase
             )
         );
 
-        $serverRequest = new ServerRequest();
-        $serverRequest = $serverRequest->withParsedBody([
+        $serverRequest = (new ServerRequest())->withParsedBody([
             'client_id'     => 'foo',
             'client_secret' => 'bar',
             'refresh_token' => $oldRefreshToken,
@@ -88,7 +88,7 @@ class RefreshTokenGrantTest extends TestCase
         ]);
 
         $responseType = new StubResponseType();
-        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new \DateInterval('PT5M'));
+        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new DateInterval('PT5M'));
 
         $this->assertInstanceOf(AccessTokenEntityInterface::class, $responseType->getAccessToken());
         $this->assertInstanceOf(RefreshTokenEntityInterface::class, $responseType->getRefreshToken());
@@ -136,8 +136,7 @@ class RefreshTokenGrantTest extends TestCase
             )
         );
 
-        $serverRequest = new ServerRequest();
-        $serverRequest = $serverRequest->withParsedBody([
+        $serverRequest = (new ServerRequest())->withParsedBody([
             'client_id'     => 'foo',
             'client_secret' => 'bar',
             'refresh_token' => $oldRefreshToken,
@@ -191,27 +190,20 @@ class RefreshTokenGrantTest extends TestCase
             )
         );
 
-        $serverRequest = new ServerRequest();
-        $serverRequest = $serverRequest->withParsedBody(
-            [
-                'client_id'     => 'foo',
-                'client_secret' => 'bar',
-                'refresh_token' => $oldRefreshToken,
-                'scope'         => 'foo',
-            ]
-        );
+        $serverRequest = (new ServerRequest())->withParsedBody([
+            'client_id'     => 'foo',
+            'client_secret' => 'bar',
+            'refresh_token' => $oldRefreshToken,
+            'scope'         => 'foo',
+        ]);
 
         $responseType = new StubResponseType();
-        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new \DateInterval('PT5M'));
+        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new DateInterval('PT5M'));
 
         $this->assertInstanceOf(AccessTokenEntityInterface::class, $responseType->getAccessToken());
         $this->assertInstanceOf(RefreshTokenEntityInterface::class, $responseType->getRefreshToken());
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
-     * @expectedExceptionCode 5
-     */
     public function testRespondToUnexpectedScope()
     {
         $client = new ClientEntity();
@@ -250,24 +242,21 @@ class RefreshTokenGrantTest extends TestCase
             )
         );
 
-        $serverRequest = new ServerRequest();
-        $serverRequest = $serverRequest->withParsedBody(
-            [
-                'client_id'     => 'foo',
-                'client_secret' => 'bar',
-                'refresh_token' => $oldRefreshToken,
-                'scope'         => 'foobar',
-            ]
-        );
+        $serverRequest = (new ServerRequest())->withParsedBody([
+            'client_id'     => 'foo',
+            'client_secret' => 'bar',
+            'refresh_token' => $oldRefreshToken,
+            'scope'         => 'foobar',
+        ]);
 
         $responseType = new StubResponseType();
-        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new \DateInterval('PT5M'));
+
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
+        $this->expectExceptionCode(5);
+
+        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new DateInterval('PT5M'));
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
-     * @expectedExceptionCode 3
-     */
     public function testRespondToRequestMissingOldToken()
     {
         $client = new ClientEntity();
@@ -284,22 +273,19 @@ class RefreshTokenGrantTest extends TestCase
         $grant->setEncryptionKey($this->cryptStub->getKey());
         $grant->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
 
-        $serverRequest = new ServerRequest();
-        $serverRequest = $serverRequest->withParsedBody(
-            [
-                'client_id'     => 'foo',
-                'client_secret' => 'bar',
-            ]
-        );
+        $serverRequest = (new ServerRequest())->withParsedBody([
+            'client_id'     => 'foo',
+            'client_secret' => 'bar',
+        ]);
 
         $responseType = new StubResponseType();
-        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new \DateInterval('PT5M'));
+
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
+        $this->expectExceptionCode(3);
+
+        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new DateInterval('PT5M'));
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
-     * @expectedExceptionCode 8
-     */
     public function testRespondToRequestInvalidOldToken()
     {
         $client = new ClientEntity();
@@ -318,23 +304,20 @@ class RefreshTokenGrantTest extends TestCase
 
         $oldRefreshToken = 'foobar';
 
-        $serverRequest = new ServerRequest();
-        $serverRequest = $serverRequest->withParsedBody(
-            [
-                'client_id'     => 'foo',
-                'client_secret' => 'bar',
-                'refresh_token' => $oldRefreshToken,
-            ]
-        );
+        $serverRequest = (new ServerRequest())->withParsedBody([
+            'client_id'     => 'foo',
+            'client_secret' => 'bar',
+            'refresh_token' => $oldRefreshToken,
+        ]);
 
         $responseType = new StubResponseType();
-        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new \DateInterval('PT5M'));
+
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
+        $this->expectExceptionCode(8);
+
+        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new DateInterval('PT5M'));
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
-     * @expectedExceptionCode 8
-     */
     public function testRespondToRequestClientMismatch()
     {
         $client = new ClientEntity();
@@ -367,23 +350,20 @@ class RefreshTokenGrantTest extends TestCase
             )
         );
 
-        $serverRequest = new ServerRequest();
-        $serverRequest = $serverRequest->withParsedBody(
-            [
-                'client_id'     => 'foo',
-                'client_secret' => 'bar',
-                'refresh_token' => $oldRefreshToken,
-            ]
-        );
+        $serverRequest = (new ServerRequest())->withParsedBody([
+            'client_id'     => 'foo',
+            'client_secret' => 'bar',
+            'refresh_token' => $oldRefreshToken,
+        ]);
 
         $responseType = new StubResponseType();
-        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new \DateInterval('PT5M'));
+
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
+        $this->expectExceptionCode(8);
+
+        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new DateInterval('PT5M'));
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
-     * @expectedExceptionCode 8
-     */
     public function testRespondToRequestExpiredToken()
     {
         $client = new ClientEntity();
@@ -413,23 +393,20 @@ class RefreshTokenGrantTest extends TestCase
             )
         );
 
-        $serverRequest = new ServerRequest();
-        $serverRequest = $serverRequest->withParsedBody(
-            [
-                'client_id'     => 'foo',
-                'client_secret' => 'bar',
-                'refresh_token' => $oldRefreshToken,
-            ]
-        );
+        $serverRequest = (new ServerRequest())->withParsedBody([
+            'client_id'     => 'foo',
+            'client_secret' => 'bar',
+            'refresh_token' => $oldRefreshToken,
+        ]);
 
         $responseType = new StubResponseType();
-        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new \DateInterval('PT5M'));
+
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
+        $this->expectExceptionCode(8);
+
+        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new DateInterval('PT5M'));
     }
 
-    /**
-     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
-     * @expectedExceptionCode 8
-     */
     public function testRespondToRequestRevokedToken()
     {
         $client = new ClientEntity();
@@ -460,16 +437,17 @@ class RefreshTokenGrantTest extends TestCase
             )
         );
 
-        $serverRequest = new ServerRequest();
-        $serverRequest = $serverRequest->withParsedBody(
-            [
-                'client_id'     => 'foo',
-                'client_secret' => 'bar',
-                'refresh_token' => $oldRefreshToken,
-            ]
-        );
+        $serverRequest = (new ServerRequest())->withParsedBody([
+            'client_id'     => 'foo',
+            'client_secret' => 'bar',
+            'refresh_token' => $oldRefreshToken,
+        ]);
 
         $responseType = new StubResponseType();
-        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new \DateInterval('PT5M'));
+
+        $this->expectException(\League\OAuth2\Server\Exception\OAuthServerException::class);
+        $this->expectExceptionCode(8);
+
+        $grant->respondToAccessTokenRequest($serverRequest, $responseType, new DateInterval('PT5M'));
     }
 }
diff --git a/tests/Middleware/AuthorizationServerMiddlewareTest.php b/tests/Middleware/AuthorizationServerMiddlewareTest.php
index fb11c483..c8ed7d1a 100644
--- a/tests/Middleware/AuthorizationServerMiddlewareTest.php
+++ b/tests/Middleware/AuthorizationServerMiddlewareTest.php
@@ -2,6 +2,7 @@
 
 namespace LeagueTests\Middleware;
 
+use DateInterval;
 use League\OAuth2\Server\AuthorizationServer;
 use League\OAuth2\Server\Exception\OAuthServerException;
 use League\OAuth2\Server\Grant\ClientCredentialsGrant;
@@ -66,7 +67,7 @@ class AuthorizationServerMiddlewareTest extends TestCase
     public function testOAuthErrorResponse()
     {
         $clientRepository = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
-        $clientRepository->method('getClientEntity')->willReturn(null);
+        $clientRepository->method('validateClient')->willReturn(false);
 
         $server = new AuthorizationServer(
             $clientRepository,
@@ -77,7 +78,7 @@ class AuthorizationServerMiddlewareTest extends TestCase
             new StubResponseType()
         );
 
-        $server->enableGrantType(new ClientCredentialsGrant(), new \DateInterval('PT1M'));
+        $server->enableGrantType(new ClientCredentialsGrant(), new DateInterval('PT1M'));
 
         $_POST['grant_type'] = 'client_credentials';
         $_POST['client_id'] = 'foo';
diff --git a/tests/Middleware/ResourceServerMiddlewareTest.php b/tests/Middleware/ResourceServerMiddlewareTest.php
index 2269c45a..4f2d3079 100644
--- a/tests/Middleware/ResourceServerMiddlewareTest.php
+++ b/tests/Middleware/ResourceServerMiddlewareTest.php
@@ -2,6 +2,8 @@
 
 namespace LeagueTests\Middleware;
 
+use DateInterval;
+use DateTimeImmutable;
 use League\OAuth2\Server\CryptKey;
 use League\OAuth2\Server\Middleware\ResourceServerMiddleware;
 use League\OAuth2\Server\Repositories\AccessTokenRepositoryInterface;
@@ -27,13 +29,13 @@ class ResourceServerMiddlewareTest extends TestCase
         $accessToken = new AccessTokenEntity();
         $accessToken->setIdentifier('test');
         $accessToken->setUserIdentifier(123);
-        $accessToken->setExpiryDateTime((new \DateTime())->add(new \DateInterval('PT1H')));
+        $accessToken->setExpiryDateTime((new DateTimeImmutable())->add(new DateInterval('PT1H')));
         $accessToken->setClient($client);
+        $accessToken->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
 
-        $token = $accessToken->convertToJWT(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
+        $token = (string) $accessToken;
 
-        $request = new ServerRequest();
-        $request = $request->withHeader('authorization', sprintf('Bearer %s', $token));
+        $request = (new ServerRequest())->withHeader('authorization', sprintf('Bearer %s', $token));
 
         $middleware = new ResourceServerMiddleware($server);
         $response = $middleware->__invoke(
@@ -62,13 +64,13 @@ class ResourceServerMiddlewareTest extends TestCase
         $accessToken = new AccessTokenEntity();
         $accessToken->setIdentifier('test');
         $accessToken->setUserIdentifier(123);
-        $accessToken->setExpiryDateTime((new \DateTime())->sub(new \DateInterval('PT1H')));
+        $accessToken->setExpiryDateTime((new DateTimeImmutable())->sub(new DateInterval('PT1H')));
         $accessToken->setClient($client);
+        $accessToken->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
 
-        $token = $accessToken->convertToJWT(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
+        $token = (string) $accessToken;
 
-        $request = new ServerRequest();
-        $request = $request->withHeader('authorization', sprintf('Bearer %s', $token));
+        $request = (new ServerRequest())->withHeader('authorization', sprintf('Bearer %s', $token));
 
         $middleware = new ResourceServerMiddleware($server);
         $response = $middleware->__invoke(
@@ -91,8 +93,7 @@ class ResourceServerMiddlewareTest extends TestCase
             'file://' . __DIR__ . '/../Stubs/public.key'
         );
 
-        $request = new ServerRequest();
-        $request = $request->withHeader('authorization', '');
+        $request = (new ServerRequest())->withHeader('authorization', '');
 
         $middleware = new ResourceServerMiddleware($server);
         $response = $middleware->__invoke(
diff --git a/tests/ResponseTypes/BearerResponseTypeTest.php b/tests/ResponseTypes/BearerResponseTypeTest.php
index 31245b07..0c4a46fc 100644
--- a/tests/ResponseTypes/BearerResponseTypeTest.php
+++ b/tests/ResponseTypes/BearerResponseTypeTest.php
@@ -2,6 +2,8 @@
 
 namespace LeagueTests\ResponseTypes;
 
+use DateInterval;
+use DateTimeImmutable;
 use League\OAuth2\Server\AuthorizationValidators\BearerTokenValidator;
 use League\OAuth2\Server\CryptKey;
 use League\OAuth2\Server\Exception\OAuthServerException;
@@ -32,14 +34,15 @@ class BearerResponseTypeTest extends TestCase
 
         $accessToken = new AccessTokenEntity();
         $accessToken->setIdentifier('abcdef');
-        $accessToken->setExpiryDateTime((new \DateTime())->add(new \DateInterval('PT1H')));
+        $accessToken->setExpiryDateTime((new DateTimeImmutable())->add(new DateInterval('PT1H')));
         $accessToken->setClient($client);
         $accessToken->addScope($scope);
+        $accessToken->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
 
         $refreshToken = new RefreshTokenEntity();
         $refreshToken->setIdentifier('abcdef');
         $refreshToken->setAccessToken($accessToken);
-        $refreshToken->setExpiryDateTime((new \DateTime())->add(new \DateInterval('PT1H')));
+        $refreshToken->setExpiryDateTime((new DateTimeImmutable())->add(new DateInterval('PT1H')));
 
         $responseType->setAccessToken($accessToken);
         $responseType->setRefreshToken($refreshToken);
@@ -54,7 +57,7 @@ class BearerResponseTypeTest extends TestCase
 
         $response->getBody()->rewind();
         $json = json_decode($response->getBody()->getContents());
-        $this->assertAttributeEquals('Bearer', 'token_type', $json);
+        $this->assertEquals('Bearer', $json->token_type);
         $this->assertObjectHasAttribute('expires_in', $json);
         $this->assertObjectHasAttribute('access_token', $json);
         $this->assertObjectHasAttribute('refresh_token', $json);
@@ -74,14 +77,15 @@ class BearerResponseTypeTest extends TestCase
 
         $accessToken = new AccessTokenEntity();
         $accessToken->setIdentifier('abcdef');
-        $accessToken->setExpiryDateTime((new \DateTime())->add(new \DateInterval('PT1H')));
+        $accessToken->setExpiryDateTime((new DateTimeImmutable())->add(new DateInterval('PT1H')));
         $accessToken->setClient($client);
         $accessToken->addScope($scope);
+        $accessToken->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
 
         $refreshToken = new RefreshTokenEntity();
         $refreshToken->setIdentifier('abcdef');
         $refreshToken->setAccessToken($accessToken);
-        $refreshToken->setExpiryDateTime((new \DateTime())->add(new \DateInterval('PT1H')));
+        $refreshToken->setExpiryDateTime((new DateTimeImmutable())->add(new DateInterval('PT1H')));
 
         $responseType->setAccessToken($accessToken);
         $responseType->setRefreshToken($refreshToken);
@@ -96,13 +100,13 @@ class BearerResponseTypeTest extends TestCase
 
         $response->getBody()->rewind();
         $json = json_decode($response->getBody()->getContents());
-        $this->assertAttributeEquals('Bearer', 'token_type', $json);
+        $this->assertEquals('Bearer', $json->token_type);
         $this->assertObjectHasAttribute('expires_in', $json);
         $this->assertObjectHasAttribute('access_token', $json);
         $this->assertObjectHasAttribute('refresh_token', $json);
 
         $this->assertObjectHasAttribute('foo', $json);
-        $this->assertAttributeEquals('bar', 'foo', $json);
+        $this->assertEquals('bar', $json->foo);
     }
 
     public function testDetermineAccessTokenInHeaderValidToken()
@@ -117,13 +121,14 @@ class BearerResponseTypeTest extends TestCase
         $accessToken = new AccessTokenEntity();
         $accessToken->setIdentifier('abcdef');
         $accessToken->setUserIdentifier(123);
-        $accessToken->setExpiryDateTime((new \DateTime())->add(new \DateInterval('PT1H')));
+        $accessToken->setExpiryDateTime((new DateTimeImmutable())->add(new DateInterval('PT1H')));
         $accessToken->setClient($client);
+        $accessToken->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
 
         $refreshToken = new RefreshTokenEntity();
         $refreshToken->setIdentifier('abcdef');
         $refreshToken->setAccessToken($accessToken);
-        $refreshToken->setExpiryDateTime((new \DateTime())->add(new \DateInterval('PT1H')));
+        $refreshToken->setExpiryDateTime((new DateTimeImmutable())->add(new DateInterval('PT1H')));
 
         $responseType->setAccessToken($accessToken);
         $responseType->setRefreshToken($refreshToken);
@@ -137,8 +142,7 @@ class BearerResponseTypeTest extends TestCase
         $authorizationValidator = new BearerTokenValidator($accessTokenRepositoryMock);
         $authorizationValidator->setPublicKey(new CryptKey('file://' . __DIR__ . '/../Stubs/public.key'));
 
-        $request = new ServerRequest();
-        $request = $request->withHeader('authorization', sprintf('Bearer %s', $json->access_token));
+        $request = (new ServerRequest())->withHeader('authorization', sprintf('Bearer %s', $json->access_token));
 
         $request = $authorizationValidator->validateAuthorization($request);
 
@@ -162,13 +166,14 @@ class BearerResponseTypeTest extends TestCase
         $accessToken = new AccessTokenEntity();
         $accessToken->setIdentifier('abcdef');
         $accessToken->setUserIdentifier(123);
-        $accessToken->setExpiryDateTime((new \DateTime())->add(new \DateInterval('PT1H')));
+        $accessToken->setExpiryDateTime((new DateTimeImmutable())->add(new DateInterval('PT1H')));
         $accessToken->setClient($client);
+        $accessToken->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
 
         $refreshToken = new RefreshTokenEntity();
         $refreshToken->setIdentifier('abcdef');
         $refreshToken->setAccessToken($accessToken);
-        $refreshToken->setExpiryDateTime((new \DateTime())->add(new \DateInterval('PT1H')));
+        $refreshToken->setExpiryDateTime((new DateTimeImmutable())->add(new DateInterval('PT1H')));
 
         $responseType->setAccessToken($accessToken);
         $responseType->setRefreshToken($refreshToken);
@@ -179,8 +184,7 @@ class BearerResponseTypeTest extends TestCase
         $authorizationValidator = new BearerTokenValidator($accessTokenRepositoryMock);
         $authorizationValidator->setPublicKey(new CryptKey('file://' . __DIR__ . '/../Stubs/public.key'));
 
-        $request = new ServerRequest();
-        $request = $request->withHeader('authorization', sprintf('Bearer %s', $json->access_token . 'foo'));
+        $request = (new ServerRequest())->withHeader('authorization', sprintf('Bearer %s', $json->access_token . 'foo'));
 
         try {
             $authorizationValidator->validateAuthorization($request);
@@ -204,13 +208,14 @@ class BearerResponseTypeTest extends TestCase
         $accessToken = new AccessTokenEntity();
         $accessToken->setIdentifier('abcdef');
         $accessToken->setUserIdentifier(123);
-        $accessToken->setExpiryDateTime((new \DateTime())->add(new \DateInterval('PT1H')));
+        $accessToken->setExpiryDateTime((new DateTimeImmutable())->add(new DateInterval('PT1H')));
         $accessToken->setClient($client);
+        $accessToken->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
 
         $refreshToken = new RefreshTokenEntity();
         $refreshToken->setIdentifier('abcdef');
         $refreshToken->setAccessToken($accessToken);
-        $refreshToken->setExpiryDateTime((new \DateTime())->add(new \DateInterval('PT1H')));
+        $refreshToken->setExpiryDateTime((new DateTimeImmutable())->add(new DateInterval('PT1H')));
 
         $responseType->setAccessToken($accessToken);
         $responseType->setRefreshToken($refreshToken);
@@ -224,8 +229,7 @@ class BearerResponseTypeTest extends TestCase
         $authorizationValidator = new BearerTokenValidator($accessTokenRepositoryMock);
         $authorizationValidator->setPublicKey(new CryptKey('file://' . __DIR__ . '/../Stubs/public.key'));
 
-        $request = new ServerRequest();
-        $request = $request->withHeader('authorization', sprintf('Bearer %s', $json->access_token));
+        $request = (new ServerRequest())->withHeader('authorization', sprintf('Bearer %s', $json->access_token));
 
         try {
             $authorizationValidator->validateAuthorization($request);
@@ -248,8 +252,7 @@ class BearerResponseTypeTest extends TestCase
         $authorizationValidator = new BearerTokenValidator($accessTokenRepositoryMock);
         $authorizationValidator->setPublicKey(new CryptKey('file://' . __DIR__ . '/../Stubs/public.key'));
 
-        $request = new ServerRequest();
-        $request = $request->withHeader('authorization', 'Bearer blah');
+        $request = (new ServerRequest())->withHeader('authorization', 'Bearer blah');
 
         try {
             $authorizationValidator->validateAuthorization($request);
@@ -272,8 +275,7 @@ class BearerResponseTypeTest extends TestCase
         $authorizationValidator = new BearerTokenValidator($accessTokenRepositoryMock);
         $authorizationValidator->setPublicKey(new CryptKey('file://' . __DIR__ . '/../Stubs/public.key'));
 
-        $request = new ServerRequest();
-        $request = $request->withHeader('authorization', 'Bearer blah.blah.blah');
+        $request = (new ServerRequest())->withHeader('authorization', 'Bearer blah.blah.blah');
 
         try {
             $authorizationValidator->validateAuthorization($request);
diff --git a/tests/Stubs/ClientEntity.php b/tests/Stubs/ClientEntity.php
index 0c6a4f9b..d908248b 100644
--- a/tests/Stubs/ClientEntity.php
+++ b/tests/Stubs/ClientEntity.php
@@ -15,8 +15,8 @@ class ClientEntity implements ClientEntityInterface
         $this->redirectUri = $uri;
     }
 
-    public function setName($name)
+    public function setConfidential()
     {
-        $this->name = $name;
+        $this->isConfidential = true;
     }
 }
diff --git a/tests/Utils/CryptKeyTest.php b/tests/Utils/CryptKeyTest.php
index 9f3f337c..e9799c08 100644
--- a/tests/Utils/CryptKeyTest.php
+++ b/tests/Utils/CryptKeyTest.php
@@ -7,11 +7,10 @@ use PHPUnit\Framework\TestCase;
 
 class CryptKeyTest extends TestCase
 {
-    /**
-     * @expectedException \LogicException
-     */
     public function testNoFile()
     {
+        $this->expectException(\LogicException::class);
+
         new CryptKey('undefined file');
     }
 
@@ -27,6 +26,11 @@ class CryptKeyTest extends TestCase
     public function testKeyFileCreation()
     {
         $keyContent = file_get_contents(__DIR__ . '/../Stubs/public.key');
+
+        if (!is_string($keyContent)) {
+            $this->fail('The public key stub is not a string');
+        }
+
         $key = new CryptKey($keyContent);
 
         $this->assertEquals(
@@ -35,6 +39,11 @@ class CryptKeyTest extends TestCase
         );
 
         $keyContent = file_get_contents(__DIR__ . '/../Stubs/private.key.crlf');
+
+        if (!is_string($keyContent)) {
+            $this->fail('The private key (crlf) stub is not a string');
+        }
+
         $key = new CryptKey($keyContent);
 
         $this->assertEquals(
diff --git a/tests/Utils/CryptTraitTest.php b/tests/Utils/CryptTraitTest.php
index c517cec2..06d0b219 100644
--- a/tests/Utils/CryptTraitTest.php
+++ b/tests/Utils/CryptTraitTest.php
@@ -10,7 +10,7 @@ class CryptTraitTest extends TestCase
 {
     protected $cryptStub;
 
-    protected function setUp()
+    protected function setUp(): void
     {
         $this->cryptStub = new CryptTraitStub();
     }