maintenance_mode_subscriber

  class: Drupal\Core\EventSubscriber\MaintenanceModeSubscriber
  arguments:
      - '@maintenance_mode'
      - '@config.factory'
      - '@string_translation'
      - '@url_generator'
      - '@current_user'
      - '@bare_html_page_renderer'
      - '@messenger'
  tags:
      - { name: event_subscriber }