# Symfony/Component/Security/Http/Firewall/LogoutListener.php

    // handle multiple logout attempts gracefully
    if ($token = $this->securityContext->getToken()) {
        foreach ($this->handlers as $handler) {
            $handler->logout($request, $response, $token);
        }
    }

    # Symfony/Bundle/SecurityBundle/DependencyInjection/SecurityExtension.php

    // Context serializer listener
    if (false === $firewall['stateless']) {
        $contextKey = $id;
        if (isset($firewall['context'])) {
            $contextKey = $firewall['context'];
        }

        $listeners[] = new Reference($this->createContextListener($container, $contextKey));
    }