code: protected function callback($middleware, ResponseInterface $response)
      {
          $middleware = is_string($middleware) ? new $middleware : $middleware;
  
          $callback = function ($request, $next = null) use ($middleware) {
              return $middleware($request, $next);
          };
  
          if ($this->approach($middleware) == self::SINGLE_PASS) {
              $callback = function ($request, $next = null) use ($middleware, $response) {
                  return $middleware($request, $response, $next);
              };
          }
  
          return $callback;
      }
docs: Returns the middleware as a single pass callable.
  
  @param  \Closure|object|string              $middleware
  @param  \Psr\Http\Message\ResponseInterface $response
  @return \Closure