code: protected function middleware(FinalCallback $callback, ServerRequestInterface $request)
      {
          $response = $this->container->get(self::RESPONSE);
  
          if (interface_exists(Application::MIDDLEWARE) === true) {
              $middleware = new Dispatcher($this->middlewares, $response);
  
              $delegate = new Delegate($callback);
  
              $result = $middleware->process($request, $delegate);
          }
  
          return isset($result) ? $result : $callback($request);
      }
docs: Dispatches the middlewares of the specified request, if there are any.
  
  @param  \Rougin\Slytherin\Application\FinalCallback $callback
  @param  \Psr\Http\Message\ServerRequestInterface    $request
  @return \Psr\Http\Message\ResponseInterface|null