public function execute(HTTPRequestCustom $request)
 {
     $event_id = $request->get_getint('event_id', 0);
     $current_user_id = AppContext::get_current_user()->get_id();
     if (!empty($event_id)) {
         $this->get_event($event_id);
         $this->check_authorizations();
         if (in_array($current_user_id, array_keys($this->event->get_participants()))) {
             CalendarService::delete_participant($event_id, $current_user_id);
             CalendarCurrentMonthEventsCache::invalidate();
         }
         $category = $this->event->get_content()->get_category();
         AppContext::get_response()->redirect($request->get_url_referrer() ? $request->get_url_referrer() : CalendarUrlBuilder::display_event($category->get_id(), $category->get_rewrited_name(), $event_id, $this->event->get_content()->get_rewrited_title()));
     } else {
         $error_controller = PHPBoostErrors::unexisting_page();
         DispatchManager::redirect($error_controller);
     }
 }