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;
  }