class CsrfAccessCheck

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);
    }

}