AcceptHeaderRoutingTestServiceProvider.php

<?php

namespace Drupal\accept_header_routing_test;

use Drupal\Core\DependencyInjection\ContainerBuilder;
use Drupal\Core\DependencyInjection\ServiceModifierInterface;

/**
 * Service provider for the accept_header_routing_test module.
 */
class AcceptHeaderRoutingTestServiceProvider implements ServiceModifierInterface {
    
    /**
     * {@inheritdoc}
     */
    public function alter(ContainerBuilder $container) {
        // Remove the basic content negotiation middleware and replace it with a
        // basic header based one.
        $container->register('http_middleware.negotiation', 'Drupal\\accept_header_routing_test\\AcceptHeaderMiddleware')
            ->addTag('http_middleware', [
            'priority' => 400,
        ]);
    }

}