diff --git a/src/Entities/Interfaces/TokenInterface.php b/src/Entities/Interfaces/TokenInterface.php
index dfa4e44e..a78db090 100644
--- a/src/Entities/Interfaces/TokenInterface.php
+++ b/src/Entities/Interfaces/TokenInterface.php
@@ -67,15 +67,6 @@ interface TokenInterface
      */
     public function addScope(ScopeEntityInterface $scope);
 
-    /**
-     * Get an associated scope by the scope's identifier.
-     *
-     * @param string $identifier
-     *
-     * @return ScopeEntityInterface|null The scope or null if not found
-     */
-    public function getScopeWithIdentifier($identifier);
-
     /**
      * Return an array of scopes associated with the token.
      *
diff --git a/src/Entities/Traits/TokenEntityTrait.php b/src/Entities/Traits/TokenEntityTrait.php
index 35230b26..e7b9d29f 100644
--- a/src/Entities/Traits/TokenEntityTrait.php
+++ b/src/Entities/Traits/TokenEntityTrait.php
@@ -38,18 +38,6 @@ trait TokenEntityTrait
         $this->scopes[$scope->getIdentifier()] = $scope;
     }
 
-    /**
-     * Get an associated scope by the scope's identifier.
-     *
-     * @param string $identifier
-     *
-     * @return ScopeEntityInterface|null The scope or null if not found
-     */
-    public function getScopeWithIdentifier($identifier)
-    {
-        return (isset($this->scopes[$identifier])) ? $this->scopes[$identifier] : null;
-    }
-
     /**
      * Return an array of scopes associated with the token.
      *
diff --git a/src/Exception/OAuthServerException.php b/src/Exception/OAuthServerException.php
index 7b8a1016..b61d1183 100644
--- a/src/Exception/OAuthServerException.php
+++ b/src/Exception/OAuthServerException.php
@@ -48,20 +48,6 @@ class OAuthServerException extends \Exception
         $this->redirectUri = $redirectUri;
     }
 
-    /**
-     * Invalid grant type error.
-     *
-     * @return static
-     */
-    public static function invalidGrantType()
-    {
-        $errorMessage = 'The provided authorization grant is invalid, expired, revoked, does not match ' .
-            'the redirection URI used in the authorization request, or was issued to another client.';
-        $hint = 'Check the `grant_type` parameter';
-
-        return new static($errorMessage, 1, 'invalid_grant', 400, $hint);
-    }
-
     /**
      * Unsupported grant type error.
      *
@@ -206,7 +192,7 @@ class OAuthServerException extends \Exception
         $headers = $this->getHttpHeaders();
 
         $payload = [
-            'error'   => $this->errorType,
+            'error'   => $this->getErrorType(),
             'message' => $this->getMessage(),
         ];
 
diff --git a/src/Middleware/AuthenticationServerMiddleware.php b/src/Middleware/AuthenticationServerMiddleware.php
index 8a68527d..4038d95e 100644
--- a/src/Middleware/AuthenticationServerMiddleware.php
+++ b/src/Middleware/AuthenticationServerMiddleware.php
@@ -47,10 +47,6 @@ class AuthenticationServerMiddleware
             // @codeCoverageIgnoreEnd
         }
 
-        if (in_array($response->getStatusCode(), [400, 401, 500])) {
-            return $response;
-        }
-
         // Pass the request and response on to the next responder in the chain
         return $next($request, $response);
     }