I might be missing something here but thet "Calendar API" exists for a long time: CalDav.
You can have .ical for a whole Calendar, not only an (offline) event. The calendar can be synced with new events, through CalDav, when they are added to the calendar you shared. You would still have to accept the prompt once but that is it.
You can have .ical for a whole Calendar, not only an (offline) event. The calendar can be synced with new events, through CalDav, when they are added to the calendar you shared. You would still have to accept the prompt once but that is it.