RegisterAccessCheck.php

<?php

/**
 * @file
 * Contains Drupal\user\Access\RegisterAccessCheck.
 */
namespace Drupal\user\Access;

use Drupal\Core\Access\AccessCheckInterface;
use Symfony\Component\Routing\Route;
use Symfony\Component\HttpFoundation\Request;

/**
 * Access check for user registration routes.
 */
class RegisterAccessCheck implements AccessCheckInterface {

  /**
   * Implements AccessCheckInterface::applies().
   */
  public function applies(Route $route) {
    return array_key_exists('_access_user_register', $route
      ->getRequirements());
  }

  /**
   * Implements AccessCheckInterface::access().
   */
  public function access(Route $route, Request $request) {
    return user_is_anonymous() && config('user.settings')
      ->get('register') != USER_REGISTER_ADMINISTRATORS_ONLY;
  }

}