diff --git a/src/Grant/AuthCodeGrant.php b/src/Grant/AuthCodeGrant.php
index fc8fec53..2d8fb5db 100644
--- a/src/Grant/AuthCodeGrant.php
+++ b/src/Grant/AuthCodeGrant.php
@@ -165,12 +165,18 @@ class AuthCodeGrant extends AbstractGrant
         // Get the required params
         $clientId = $this->server->getRequest()->request->get('client_id', null);
         if (is_null($clientId)) {
-            throw new Exception\InvalidRequestException('client_id');
+            $clientId = $this->server->getRequest()->getUser();
+            if (is_null($clientId)) {
+                throw new Exception\InvalidRequestException('client_id');
+            }
         }
 
         $clientSecret = $this->server->getRequest()->request->get('client_secret', null);
         if (is_null($clientSecret)) {
-            throw new Exception\InvalidRequestException('client_secret');
+            $clientSecret = $this->server->getRequest()->getPassword();
+            if (is_null($clientSecret)) {
+                throw new Exception\InvalidRequestException('client_secret');
+            }
         }
 
         $redirectUri = $this->server->getRequest()->request->get('redirect_uri', null);
diff --git a/src/Grant/ClientCredentialsGrant.php b/src/Grant/ClientCredentialsGrant.php
index 786d5d2c..442d6f84 100644
--- a/src/Grant/ClientCredentialsGrant.php
+++ b/src/Grant/ClientCredentialsGrant.php
@@ -56,12 +56,18 @@ class ClientCredentialsGrant extends AbstractGrant
          // Get the required params
         $clientId = $this->server->getRequest()->request->get('client_id', null);
         if (is_null($clientId)) {
-            throw new Exception\InvalidRequestException('client_id');
+            $clientId = $this->server->getRequest()->getUser();
+            if (is_null($clientId)) {
+                throw new Exception\InvalidRequestException('client_id');
+            }
         }
 
         $clientSecret = $this->server->getRequest()->request->get('client_secret', null);
         if (is_null($clientSecret)) {
-            throw new Exception\InvalidRequestException('client_secret');
+            $clientSecret = $this->server->getRequest()->getPassword();
+            if (is_null($clientSecret)) {
+                throw new Exception\InvalidRequestException('client_secret');
+            }
         }
 
         // Validate client ID and client secret
diff --git a/src/Grant/PasswordGrant.php b/src/Grant/PasswordGrant.php
index 9c2b27e3..6e90aa19 100644
--- a/src/Grant/PasswordGrant.php
+++ b/src/Grant/PasswordGrant.php
@@ -80,12 +80,18 @@ class PasswordGrant extends AbstractGrant
         // Get the required params
         $clientId = $this->server->getRequest()->request->get('client_id', null);
         if (is_null($clientId)) {
-            throw new Exception\InvalidRequestException('client_id');
+            $clientId = $this->server->getRequest()->getUser();
+            if (is_null($clientId)) {
+                throw new Exception\InvalidRequestException('client_id');
+            }
         }
 
         $clientSecret = $this->server->getRequest()->request->get('client_secret', null);
         if (is_null($clientSecret)) {
-            throw new Exception\InvalidRequestException('client_secret');
+            $clientSecret = $this->server->getRequest()->getPassword();
+            if (is_null($clientSecret)) {
+                throw new Exception\InvalidRequestException('client_secret');
+            }
         }
 
         // Validate client ID and client secret
diff --git a/src/Grant/RefreshTokenGrant.php b/src/Grant/RefreshTokenGrant.php
index 01f5e695..f757560c 100644
--- a/src/Grant/RefreshTokenGrant.php
+++ b/src/Grant/RefreshTokenGrant.php
@@ -60,12 +60,18 @@ class RefreshTokenGrant extends AbstractGrant
     {
         $clientId = $this->server->getRequest()->request->get('client_id', null);
         if (is_null($clientId)) {
-            throw new Exception\InvalidRequestException('client_id');
+            $clientId = $this->server->getRequest()->getUser();
+            if (is_null($clientId)) {
+                throw new Exception\InvalidRequestException('client_id');
+            }
         }
 
         $clientSecret = $this->server->getRequest()->request->get('client_secret', null);
         if (is_null($clientSecret)) {
-            throw new Exception\InvalidRequestException('client_secret');
+            $clientSecret = $this->server->getRequest()->getPassword();
+            if (is_null($clientSecret)) {
+                throw new Exception\InvalidRequestException('client_secret');
+            }
         }
 
         // Validate client ID and client secret