JMAP[0], which has in-progress specs for calendar and contacts, is supposed to save us. It can't happen soon enough - if it happens at all.

[0] https://jmap.io/spec.html

There is at least https://jmap.io/spec-calendars.html just adoption is a bit low for now but I hope it will gain more traction the next years.

what you mean? a new http extension to access/author resources?