class AccessDeniedSubscriber

class AccessDeniedSubscriber implements EventSubscriberInterface {

  /**
   * The current user.
   *
   * @var \Drupal\Core\Session\AccountInterface
   */
  protected $account;

  /**
   * Constructs a new redirect subscriber.
   *
   * @param \Drupal\Core\Session\AccountInterface $account
   *   The current user.
   */
  public function __construct(AccountInterface $account) {
    $this->account = $account;
  }

  /**
   * Redirects users when access is denied.
   *
   * @param \Symfony\Component\HttpKernel\Event\ExceptionEvent $event
   *   The event to process.
   */
  public function onException(ExceptionEvent $event) {
    $exception = $event
      ->getThrowable();
    if ($exception instanceof AccessDeniedHttpException) {
      $route_name = RouteMatch::createFromRequest($event
        ->getRequest())
        ->getRouteName();
      $redirect_url = NULL;
      if ($this->account
        ->isAuthenticated()) {
        switch ($route_name) {
          case 'user.login':

            // Redirect an authenticated user to the profile page.
            $redirect_url = Url::fromRoute('entity.user.canonical', [
              'user' => $this->account
                ->id(),
            ], [
              'absolute' => TRUE,
            ]);
            break;
          case 'user.register':

            // Redirect an authenticated user to the profile form.
            $redirect_url = Url::fromRoute('entity.user.edit_form', [
              'user' => $this->account
                ->id(),
            ], [
              'absolute' => TRUE,
            ]);
            break;
        }
      }
      elseif ($route_name === 'user.page') {
        $redirect_url = Url::fromRoute('user.login', [], [
          'absolute' => TRUE,
        ]);
      }
      elseif ($route_name === 'user.logout') {
        $redirect_url = Url::fromRoute('<front>', [], [
          'absolute' => TRUE,
        ]);
      }
      if ($redirect_url) {
        $event
          ->setResponse(new RedirectResponse($redirect_url
          ->toString()));
      }
    }
  }

  /**
   * {@inheritdoc}
   */
  public static function getSubscribedEvents() : array {

    // Use a higher priority than
    // \Drupal\Core\EventSubscriber\ExceptionLoggingSubscriber, because there's
    // no need to log the exception if we can redirect.
    $events[KernelEvents::EXCEPTION][] = [
      'onException',
      75,
    ];
    return $events;
  }

}