/**
  * Validates a public auth token. Returns User object on success, otherwise false.
  *
  * @param $authTokenPayload
  * @return bool|Authenticatable
  */
 public function validate($authTokenPayload)
 {
     if ($authTokenPayload == null) {
         return false;
     }
     $tokenResponse = $this->tokens->find($authTokenPayload);
     if ($tokenResponse == null) {
         return false;
     }
     $user = $this->users->retrieveByID($tokenResponse->getAuthIdentifier());
     if ($user == null) {
         return false;
     }
     return $user;
 }