RedirectResponseSubscriber::checkRedirectUrl

public RedirectResponseSubscriber::checkRedirectUrl(FilterResponseEvent $event)

public function checkRedirectUrl(FilterResponseEvent $event) {
  $response = $event->getResponse();
  if ($response instanceof RedirectResponse) {
    $request = $event->getRequest();

    // Let the 'destination' query parameter override the redirect target.
    // If $response is already a SecuredRedirectResponse, it might reject the
    // new target as invalid, in which case proceed with the old target.
    $destination = $request->query->get('destination');
    if ($destination) {
      // The 'Location' HTTP header must always be absolute.
      $destination = $this->getDestinationAsAbsoluteUrl($destination, $request->getSchemeAndHttpHost());
      try {
        $response->setTargetUrl($destination);
      }
      catch (\InvalidArgumentException $e) {
      }
    }

    // Regardless of whether the target is the original one or the overridden
    // destination, ensure that all redirects are safe.
    if (!($response instanceof SecuredRedirectResponse)) {
      try {
        // SecuredRedirectResponse is an abstract class that requires a
        // concrete implementation. Default to LocalRedirectResponse, which
        // considers only redirects to within the same site as safe.
        $safe_response = LocalRedirectResponse::createFromRedirectResponse($response);
        $safe_response->setRequestContext($this->requestContext);
      }
      catch (\InvalidArgumentException $e) {
        // If the above failed, it's because the redirect target wasn't
        // local. Do not follow that redirect. Display an error message
        // instead. We're already catching one exception, so trigger_error()
        // rather than throw another one.
        // We don't throw an exception, because this is a client error rather than a
        // server error.
        $message = 'Redirects to external URLs are not allowed by default, use \Drupal\Core\Routing\TrustedRedirectResponse for it.';
        trigger_error($message, E_USER_ERROR);
        $safe_response = new Response($message, 400);
      }
      $event->setResponse($safe_response);
    }
  }
}