stack.php

$stack = function () use ($app) {
   $args = func_get_args();
   return function() use ($app, $args){
      $req = $app['request'];
      $res = new \Symfony\Component\HttpFoundation\Response;
      $cb = false;
      foreach($args as $mw){
         $cb = function($req, $res) use ($mw, $cb){
            return $cb($req, $res, function($req, $res, $cb){
               if( is_instance($mw, 'CallableMiddleware') ) {
                  return $mw->call($req, $res, $cb);
               } else {
                  return $mw($req, $res, $cb);
               }
            });
         }
      }
      return $cb($req, $res);
   }
}

$reqUser = function($req, $res, $cb){
   if ($req['user']) return $cb($req, $res);
   $res->setForbidden();
}

$app->get('/', $stack($reqUser, function($req, $res){
    return "Hello world";
}));