Proton does not currently offer CalDAV or CardDAV services, however there is a highly modular platform used by many large companies that allows for simple integration into third party authentication services: [Baikal](https://sabre.io/baikal/), backed by [sabre/dav](https://sabre.io/dav/). Does Proton have a published API that could be leveraged for authentication? sabre/dav already has a plugin for IMAP, but of course that can't put targeted to Proton. *Many* services offer access to their IDP these days, I'm wondering if there is a service like this from Proton as well?