MaintenanceModeSubscriber::onKernelRequestMaintenance

public MaintenanceModeSubscriber::onKernelRequestMaintenance(GetResponseEvent $event)

public function onKernelRequestMaintenance(GetResponseEvent $event) {
  $request = $event->getRequest();
  $route_match = RouteMatch::createFromRequest($request);
  if ($this->maintenanceMode->applies($route_match)) {
    // If the site is offline, log out unprivileged users.
    if ($this->account->isAuthenticated() && !$this->maintenanceMode->exempt($this->account)) {
      user_logout();
      // Redirect to homepage.
      $event->setResponse($this->redirect($this->url('<front>')));
    }
  }
}