Issue #3347067 by danflanagan8, _pratik_, smustgrave, longwave:...

use Symfony\Component\HttpFoundation\Request;

/**

 * Allows access to routes to be controlled by a '_csrf_token' parameter.

 * Access protection against CSRF attacks.

 *

 * To use this check, add a "token" GET parameter to URLs of which the value is

 * a token generated by \Drupal::csrfToken()->get() using the same value as the

 * "_csrf_token" parameter in the route.

 * 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 {