diff --git a/src/Grant/AbstractGrant.php b/src/Grant/AbstractGrant.php
index cdbd04ff..45c8fc2a 100644
--- a/src/Grant/AbstractGrant.php
+++ b/src/Grant/AbstractGrant.php
@@ -35,11 +35,6 @@ abstract class AbstractGrant implements GrantTypeInterface
 
     const SCOPE_DELIMITER_STRING = ' ';
 
-    /**
-     * @var ServerRequestInterface
-     */
-    protected $request;
-
     /**
      * @var ClientRepositoryInterface
      */
@@ -166,7 +161,7 @@ abstract class AbstractGrant implements GrantTypeInterface
         );
 
         if (!$client instanceof ClientEntityInterface) {
-            $this->getEmitter()->emit(new RequestEvent('client.authentication.failed', $request));
+            $this->getEmitter()->emit(new RequestEvent(RequestEvent::CLIENT_AUTHENTICATION_FAILED, $request));
             throw OAuthServerException::invalidClient();
         }
 
@@ -177,13 +172,13 @@ abstract class AbstractGrant implements GrantTypeInterface
                 is_string($client->getRedirectUri())
                 && (strcmp($client->getRedirectUri(), $redirectUri) !== 0)
             ) {
-                $this->getEmitter()->emit(new RequestEvent('client.authentication.failed', $request));
+                $this->getEmitter()->emit(new RequestEvent(RequestEvent::CLIENT_AUTHENTICATION_FAILED, $request));
                 throw OAuthServerException::invalidClient();
             } elseif (
                 is_array($client->getRedirectUri())
                 && in_array($redirectUri, $client->getRedirectUri()) === false
             ) {
-                $this->getEmitter()->emit(new RequestEvent('client.authentication.failed', $request));
+                $this->getEmitter()->emit(new RequestEvent(RequestEvent::CLIENT_AUTHENTICATION_FAILED, $request));
                 throw OAuthServerException::invalidClient();
             }
         }
diff --git a/src/Grant/AuthCodeGrant.php b/src/Grant/AuthCodeGrant.php
index b9416a2b..9216e167 100644
--- a/src/Grant/AuthCodeGrant.php
+++ b/src/Grant/AuthCodeGrant.php
@@ -176,7 +176,7 @@ class AuthCodeGrant extends AbstractAuthorizeGrant
         );
 
         if ($client instanceof ClientEntityInterface === false) {
-            $this->getEmitter()->emit(new RequestEvent('client.authentication.failed', $request));
+            $this->getEmitter()->emit(new RequestEvent(RequestEvent::CLIENT_AUTHENTICATION_FAILED, $request));
             throw OAuthServerException::invalidClient();
         }
 
@@ -186,13 +186,13 @@ class AuthCodeGrant extends AbstractAuthorizeGrant
                 is_string($client->getRedirectUri())
                 && (strcmp($client->getRedirectUri(), $redirectUri) !== 0)
             ) {
-                $this->getEmitter()->emit(new RequestEvent('client.authentication.failed', $request));
+                $this->getEmitter()->emit(new RequestEvent(RequestEvent::CLIENT_AUTHENTICATION_FAILED, $request));
                 throw OAuthServerException::invalidClient();
             } elseif (
                 is_array($client->getRedirectUri())
                 && in_array($redirectUri, $client->getRedirectUri()) === false
             ) {
-                $this->getEmitter()->emit(new RequestEvent('client.authentication.failed', $request));
+                $this->getEmitter()->emit(new RequestEvent(RequestEvent::CLIENT_AUTHENTICATION_FAILED, $request));
                 throw OAuthServerException::invalidClient();
             }
         }
diff --git a/src/Grant/ImplicitGrant.php b/src/Grant/ImplicitGrant.php
index f3a74ced..0bd33fa6 100644
--- a/src/Grant/ImplicitGrant.php
+++ b/src/Grant/ImplicitGrant.php
@@ -123,7 +123,7 @@ class ImplicitGrant extends AbstractAuthorizeGrant
         );
 
         if ($client instanceof ClientEntityInterface === false) {
-            $this->getEmitter()->emit(new RequestEvent('client.authentication.failed', $request));
+            $this->getEmitter()->emit(new RequestEvent(RequestEvent::CLIENT_AUTHENTICATION_FAILED, $request));
             throw OAuthServerException::invalidClient();
         }
 
@@ -133,13 +133,13 @@ class ImplicitGrant extends AbstractAuthorizeGrant
                 is_string($client->getRedirectUri())
                 && (strcmp($client->getRedirectUri(), $redirectUri) !== 0)
             ) {
-                $this->getEmitter()->emit(new RequestEvent('client.authentication.failed', $request));
+                $this->getEmitter()->emit(new RequestEvent(RequestEvent::CLIENT_AUTHENTICATION_FAILED, $request));
                 throw OAuthServerException::invalidClient();
             } elseif (
                 is_array($client->getRedirectUri())
                 && in_array($redirectUri, $client->getRedirectUri()) === false
             ) {
-                $this->getEmitter()->emit(new RequestEvent('client.authentication.failed', $request));
+                $this->getEmitter()->emit(new RequestEvent(RequestEvent::CLIENT_AUTHENTICATION_FAILED, $request));
                 throw OAuthServerException::invalidClient();
             }
         }
diff --git a/src/Grant/PasswordGrant.php b/src/Grant/PasswordGrant.php
index f87fc6ea..86ba1e32 100644
--- a/src/Grant/PasswordGrant.php
+++ b/src/Grant/PasswordGrant.php
@@ -92,7 +92,7 @@ class PasswordGrant extends AbstractGrant
             $client
         );
         if (!$user instanceof UserEntityInterface) {
-            $this->getEmitter()->emit(new RequestEvent('user.authentication.failed', $request));
+            $this->getEmitter()->emit(new RequestEvent(RequestEvent::USER_AUTHENTICATION_FAILED, $request));
 
             throw OAuthServerException::invalidCredentials();
         }
diff --git a/src/Grant/RefreshTokenGrant.php b/src/Grant/RefreshTokenGrant.php
index 0d65fae6..d4d693a6 100644
--- a/src/Grant/RefreshTokenGrant.php
+++ b/src/Grant/RefreshTokenGrant.php
@@ -107,7 +107,7 @@ class RefreshTokenGrant extends AbstractGrant
 
         $refreshTokenData = json_decode($refreshToken, true);
         if ($refreshTokenData['client_id'] !== $clientId) {
-            $this->getEmitter()->emit(new RequestEvent('refresh_token.client.failed', $request));
+            $this->getEmitter()->emit(new RequestEvent(RequestEvent::REFRESH_TOKEN_CLIENT_FAILED, $request));
             throw OAuthServerException::invalidRefreshToken('Token is not linked to client');
         }
 
diff --git a/src/RequestEvent.php b/src/RequestEvent.php
index f6cf4d92..42ce47b2 100644
--- a/src/RequestEvent.php
+++ b/src/RequestEvent.php
@@ -13,6 +13,10 @@ use Psr\Http\Message\ServerRequestInterface;
 
 class RequestEvent extends Event
 {
+    const CLIENT_AUTHENTICATION_FAILED = 'client.authentication.failed';
+    const USER_AUTHENTICATION_FAILED = 'user.authentication.failed';
+    const REFRESH_TOKEN_CLIENT_FAILED = 'refresh_token.client.failed';
+
     /**
      * @var \Psr\Http\Message\ServerRequestInterface
      */