Symfony JSON logout (json_logout, logout via AJAX call)

LogoutSubscriber.php

<?php

declare(strict_types=1);

namespace App\EventSubscriber;

use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\Security\Http\Event\LogoutEvent;

/**
 * Logout event subscriber.
 *
 * @author Hans Grinwis <hans@kwootjes.nl>
 */
final class LogoutSubscriber implements EventSubscriberInterface
{
    public static function getSubscribedEvents(): array
    {
        return [LogoutEvent::class => 'onLogout'];
    }

    public function onLogout(LogoutEvent $event): void
    {
        // json logout?
        if (str_contains($event->getRequest()->getPreferredFormat(), 'json')) {
            // 204 No Content
            $event->setResponse(new Response(null, Response::HTTP_NO_CONTENT));
        }

        // else let logout continue with redirect
    }
}

Please note that this invalidates the session, but it does not change local app state!

Also note that it seems to conflicts with explicitly setting security.firewalls.main.logout.target in Symfony 5.1. (See this.)