diff --git a/src/Grant/AuthCodeGrant.php b/src/Grant/AuthCodeGrant.php
index 8ac69270..e8c5d612 100644
--- a/src/Grant/AuthCodeGrant.php
+++ b/src/Grant/AuthCodeGrant.php
@@ -166,20 +166,15 @@ class AuthCodeGrant extends AbstractGrant
     public function completeFlow()
     {
         // Get the required params
-        $clientId = $this->server->getRequest()->request->get('client_id', null);
+        $clientId = $this->server->getRequest()->request->get('client_id', $this->server->getRequest()->getUser());
         if (is_null($clientId)) {
-            $clientId = $this->server->getRequest()->getUser();
-            if (is_null($clientId)) {
-                throw new Exception\InvalidRequestException('client_id');
-            }
+            throw new Exception\InvalidRequestException('client_id');
         }
 
-        $clientSecret = $this->server->getRequest()->request->get('client_secret', null);
+        $clientSecret = $this->server->getRequest()->request->get('client_secret',
+            $this->server->getRequest()->getPassword());
         if (is_null($clientSecret)) {
-            $clientSecret = $this->server->getRequest()->getPassword();
-            if (is_null($clientSecret)) {
-                throw new Exception\InvalidRequestException('client_secret');
-            }
+            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 6e937103..21669d9b 100644
--- a/src/Grant/ClientCredentialsGrant.php
+++ b/src/Grant/ClientCredentialsGrant.php
@@ -55,20 +55,15 @@ class ClientCredentialsGrant extends AbstractGrant
     public function completeFlow()
     {
         // Get the required params
-        $clientId = $this->server->getRequest()->request->get('client_id', null);
+        $clientId = $this->server->getRequest()->request->get('client_id', $this->server->getRequest()->getUser());
         if (is_null($clientId)) {
-            $clientId = $this->server->getRequest()->getUser();
-            if (is_null($clientId)) {
-                throw new Exception\InvalidRequestException('client_id');
-            }
+            throw new Exception\InvalidRequestException('client_id');
         }
 
-        $clientSecret = $this->server->getRequest()->request->get('client_secret', null);
+        $clientSecret = $this->server->getRequest()->request->get('client_secret',
+            $this->server->getRequest()->getPassword());
         if (is_null($clientSecret)) {
-            $clientSecret = $this->server->getRequest()->getPassword();
-            if (is_null($clientSecret)) {
-                throw new Exception\InvalidRequestException('client_secret');
-            }
+            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 496d3ace..8130ade1 100644
--- a/src/Grant/PasswordGrant.php
+++ b/src/Grant/PasswordGrant.php
@@ -80,20 +80,15 @@ class PasswordGrant extends AbstractGrant
     public function completeFlow()
     {
         // Get the required params
-        $clientId = $this->server->getRequest()->request->get('client_id', null);
+        $clientId = $this->server->getRequest()->request->get('client_id', $this->server->getRequest()->getUser());
         if (is_null($clientId)) {
-            $clientId = $this->server->getRequest()->getUser();
-            if (is_null($clientId)) {
-                throw new Exception\InvalidRequestException('client_id');
-            }
+            throw new Exception\InvalidRequestException('client_id');
         }
 
-        $clientSecret = $this->server->getRequest()->request->get('client_secret', null);
+        $clientSecret = $this->server->getRequest()->request->get('client_secret',
+            $this->server->getRequest()->getPassword());
         if (is_null($clientSecret)) {
-            $clientSecret = $this->server->getRequest()->getPassword();
-            if (is_null($clientSecret)) {
-                throw new Exception\InvalidRequestException('client_secret');
-            }
+            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 a5e23385..c12c62a9 100644
--- a/src/Grant/RefreshTokenGrant.php
+++ b/src/Grant/RefreshTokenGrant.php
@@ -58,20 +58,15 @@ class RefreshTokenGrant extends AbstractGrant
      */
     public function completeFlow()
     {
-        $clientId = $this->server->getRequest()->request->get('client_id', null);
+        $clientId = $this->server->getRequest()->request->get('client_id', $this->server->getRequest()->getUser());
         if (is_null($clientId)) {
-            $clientId = $this->server->getRequest()->getUser();
-            if (is_null($clientId)) {
-                throw new Exception\InvalidRequestException('client_id');
-            }
+            throw new Exception\InvalidRequestException('client_id');
         }
 
-        $clientSecret = $this->server->getRequest()->request->get('client_secret', null);
+        $clientSecret = $this->server->getRequest()->request->get('client_secret',
+            $this->server->getRequest()->getPassword());
         if (is_null($clientSecret)) {
-            $clientSecret = $this->server->getRequest()->getPassword();
-            if (is_null($clientSecret)) {
-                throw new Exception\InvalidRequestException('client_secret');
-            }
+            throw new Exception\InvalidRequestException('client_secret');
         }
 
         // Validate client ID and client secret