/**
  * abort the action if the user is invalid
  *
  * @param Tx_CzSimpleCal_Domain_Model_Event $event The event
  */
 protected function abortOnInvalidUser($event)
 {
     if (!$event->getCruserFe() || $this->getFrontendUserId() == null || $event->getCruserFe() != $this->getFrontendUserId()) {
         $this->throwStatus(403, 'You are not allowed to do this.');
     }
 }