hook_init() 〜 drupal_goto() を drupal8でやる方法

modules/custom/your_module/your_module.services.yml

services:
  your_module.event_subscriber:
    class: Drupal\your_module\EventSubscriber\YourModuleSubscriber
    tags:
      - {name: event_subscriber}

modules/custom/your_module/src/EventSubscriber/Your_moduleSubscriber.php

<?php

namespace Drupal\your_module\EventSubscriber;

use Symfony\Component\HttpFoundation\RedirectResponse;
use Symfony\Component\HttpKernel\KernelEvents;
use Symfony\Component\HttpKernel\Event\GetResponseEvent;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;

class YourModuleSubscriber implements EventSubscriberInterface {

  public function checkForRedirection(GetResponseEvent $event) {
    // 参考）一部の例外を除いて匿名ユーザーはloginページに飛ばす
    if (\Drupal::currentUser()->isAnonymous()) {
      if (!preg_match('!^(/user/|/sended-onetime-link-mail)!', $_SERVER['REQUEST_URI'])) {
        $path = \Drupal\Core\Url::fromUserInput('/user/login');
        $response = new RedirectResponse($path->toString());
        $response->send();
      }
    }
  }

  /**
   * {@inheritdoc}
   */
  public static function getSubscribedEvents() {
    $events[KernelEvents::REQUEST][] = array('checkForRedirection');
    return $events;
  }

}