d8-calendar-ror/calendar_ror.routing.yml

calendar_ror.ics:
    path: '/calendar/calendar.ics'
    defaults:
        _controller: '\Drupal\calendar_ror\Controller\CalendarRorController::ics'
        _title: 'Global calendar'
    requirements:
        _access: 'TRUE'
    options:
        no_cache: 'TRUE'