ReverseProxyMiddleware.php

<?php

namespace Drupal\Core\StackMiddleware;

use Drupal\Core\Site\Settings;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\HttpKernel\HttpKernelInterface;

/**
 * Provides support for reverse proxies.
 */
class ReverseProxyMiddleware implements HttpKernelInterface {
    
    /**
     * The decorated kernel.
     *
     * @var \Symfony\Component\HttpKernel\HttpKernelInterface
     */
    protected $httpKernel;
    
    /**
     * The site settings.
     *
     * @var \Drupal\Core\Site\Settings
     */
    protected $settings;
    
    /**
     * Constructs a ReverseProxyMiddleware object.
     *
     * @param \Symfony\Component\HttpKernel\HttpKernelInterface $http_kernel
     *   The decorated kernel.
     * @param \Drupal\Core\Site\Settings $settings
     *   The site settings.
     */
    public function __construct(HttpKernelInterface $http_kernel, Settings $settings) {
        $this->httpKernel = $http_kernel;
        $this->settings = $settings;
    }
    
    /**
     * {@inheritdoc}
     */
    public function handle(Request $request, $type = self::MAIN_REQUEST, $catch = TRUE) : Response {
        // Initialize proxy settings.
        static::setSettingsOnRequest($request, $this->settings);
        return $this->httpKernel
            ->handle($request, $type, $catch);
    }
    
    /**
     * Sets reverse proxy settings on Request object.
     *
     * @param \Symfony\Component\HttpFoundation\Request $request
     *   A Request instance.
     * @param \Drupal\Core\Site\Settings $settings
     *   The site settings.
     */
    public static function setSettingsOnRequest(Request $request, Settings $settings) {
        // Initialize proxy settings.
        if ($settings->get('reverse_proxy', FALSE)) {
            $proxies = $settings->get('reverse_proxy_addresses', []);
            if (count($proxies) > 0) {
                // Set the default value. This is the most relaxed setting possible and
                // not recommended for production.
                $trusted_header_set = Request::HEADER_X_FORWARDED_FOR | Request::HEADER_X_FORWARDED_HOST | Request::HEADER_X_FORWARDED_PORT | Request::HEADER_X_FORWARDED_PROTO | Request::HEADER_FORWARDED;
                $request::setTrustedProxies($proxies, $settings->get('reverse_proxy_trusted_headers', $trusted_header_set));
            }
        }
    }

}