UserRouteAlterSubscriber.php

<?php

namespace Drupal\serialization\EventSubscriber;

use Drupal\Core\Routing\RouteBuildEvent;
use Drupal\Core\Routing\RoutingEvents;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;

/**
 * Alters user authentication routes to support additional serialization formats.
 */
class UserRouteAlterSubscriber implements EventSubscriberInterface {
    
    /**
     * The available serialization formats.
     *
     * @var array
     */
    protected $serializerFormats = [];
    
    /**
     * UserRouteAlterSubscriber constructor.
     *
     * @param array $serializer_formats
     *   The available serializer formats.
     */
    public function __construct(array $serializer_formats) {
        $this->serializerFormats = $serializer_formats;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function getSubscribedEvents() : array {
        $events[RoutingEvents::ALTER][] = 'onRoutingAlterAddFormats';
        return $events;
    }
    
    /**
     * Adds supported formats to the user authentication HTTP routes.
     *
     * @param \Drupal\Core\Routing\RouteBuildEvent $event
     *   The event to process.
     */
    public function onRoutingAlterAddFormats(RouteBuildEvent $event) {
        $route_names = [
            'user.login_status.http',
            'user.login.http',
            'user.logout.http',
            'user.pass.http',
        ];
        $routes = $event->getRouteCollection();
        foreach ($route_names as $route_name) {
            if ($route = $routes->get($route_name)) {
                $formats = explode('|', $route->getRequirement('_format'));
                $formats = array_unique(array_merge($formats, $this->serializerFormats));
                $route->setRequirement('_format', implode('|', $formats));
            }
        }
    }

}