/**
  * @param SS_HTTPRequest $r
  * @return mixed
  */
 public function success(SS_HTTPRequest $r)
 {
     if (!SecurityToken::inst()->check($r->getVar('key'))) {
         $this->httpError(404);
     }
     $material = PresentationSlide::get()->byID($r->getVar('material'));
     if (!$material) {
         $this->httpError(404);
     }
     return $this->customise(['Material' => $material, 'Presentation' => $this->presentation])->renderWith(['PresentationSlideSubmissionController_success', 'Page']);
 }