/**
  * @return \Gumer\PSN\Authentication\UserInterface
  * @throws \RuntimeException
  */
 public function user()
 {
     if (!$this->user) {
         if (!($user = $this->manager->user())) {
             throw new RuntimeException('The request object requires a valid user instance for the request to be authenticated.');
         }
         $this->user = $user;
     }
     return $this->user;
 }