code: public function getAction($_format)
      {
          if ('json' === $_format) {
              $value = json_encode($this->jwkset);
              $ct = 'application/jwk-set+json; charset=UTF-8';
          } else {
              $value = json_encode($this->jwkset->toPEM());
              $ct = 'application/json; charset=UTF-8';
          }
  
          return new Response($value, Response::HTTP_OK, ['content-type' => $ct]);
      }
docs: @param string $_format
  
  @return \Symfony\Component\HttpFoundation\Response