CsrfAccessCheck.php

<?php

namespace Drupal\Core\Access;

use Drupal\Core\Routing\Access\AccessInterface as RoutingAccessInterface;
use Drupal\Core\Routing\RouteMatchInterface;
use Symfony\Component\Routing\Route;
use Symfony\Component\HttpFoundation\Request;

/**
 * Access protection against CSRF attacks.
 *
 * The CsrfAccessCheck is added to any route with the '_csrf_token' route
 * requirement. If a link/url to a protected route is generated using the
 * url_generator service, a valid token will be added automatically. Otherwise,
 * a valid token can be generated by the csrf_token service using the route's
 * path (without leading slash) as the argument when generating the token. This
 * token can then be added as the 'token' query parameter when accessing the
 * protected route.
 *
 * @see \Drupal\Core\Access\RouteProcessorCsrf
 * @see \Drupal\Core\Access\CsrfTokenGenerator
 * @see https://www.drupal.org/docs/8/api/routing-system/access-checking-on-routes/csrf-access-checking
 */
class CsrfAccessCheck implements RoutingAccessInterface {
    
    /**
     * The CSRF token generator.
     *
     * @var \Drupal\Core\Access\CsrfTokenGenerator
     */
    protected $csrfToken;
    
    /**
     * Constructs a CsrfAccessCheck object.
     *
     * @param \Drupal\Core\Access\CsrfTokenGenerator $csrf_token
     *   The CSRF token generator.
     */
    public function __construct(CsrfTokenGenerator $csrf_token) {
        $this->csrfToken = $csrf_token;
    }
    
    /**
     * Checks access based on a CSRF token for the request.
     *
     * @param \Symfony\Component\Routing\Route $route
     *   The route to check against.
     * @param \Symfony\Component\HttpFoundation\Request $request
     *   The request object.
     * @param \Drupal\Core\Routing\RouteMatchInterface $route_match
     *   The route match object.
     *
     * @return \Drupal\Core\Access\AccessResultInterface
     *   The access result.
     */
    public function access(Route $route, Request $request, RouteMatchInterface $route_match) {
        $parameters = $route_match->getRawParameters();
        $path = ltrim($route->getPath(), '/');
        // Replace the path parameters with values from the parameters array.
        foreach ($parameters as $param => $value) {
            $path = str_replace("{{$param}}", $value, $path);
        }
        if ($this->csrfToken
            ->validate($request->query
            ->get('token', ''), $path)) {
            $result = AccessResult::allowed();
        }
        else {
            $result = AccessResult::forbidden($request->query
                ->has('token') ? "'csrf_token' URL query argument is invalid." : "'csrf_token' URL query argument is missing.");
        }
        // Not cacheable because the CSRF token is highly dynamic.
        return $result->setCacheMaxAge(0);
    }

}