Check explicitly for an instance of UserInterface

Author: weierophinney

src/AuthorizationMiddleware.php

@@ -39,7 +39,7 @@ public function __construct(AuthorizationInterface $authorization, ResponseInter
     public function process(ServerRequestInterface $request, HandlerInterface $handler)
     {
         $user = $request->getAttribute(UserInterface::class, false);
-        if (false === $user) {
+        if (! $user instanceof UserInterface) {
             return $this->responsePrototype->withStatus(401);
         }