Allow oauth2 for other services than google and fastmail

[iMartyn]

Problem scope

• I'm sure that this is a DAVx⁵ problem.

App version

• I'm using the latest available DAVx⁵ version.

Android version and device/firmware type

Android 14 (Lineage 22)

Steps to reproduce

1. Run a DAV server behind some kind of auth2 proxy (in my case Xandikos behind oauth2-proxy)
2. Attempt to use the dav server

Actual result

DavX5 claims there is no CalDAV or CardDAV server at the url

Expected result

An oauth flow to occur - open the embedded browser like google or fastmail (I assume, I don't connect these services to my phone) does.

Further info

I suspect this requires a separate login type in the list (url and username; email address; advanced login) or an option within the advanced login to trigger an oauth flow.

More and more services are going oauth2 so having the ability to manually configure as oauth rather than a fixed list would be good imo.

[devvv4ever]

A generic "OAUth2" login would be useful of course. However I'm not sure but wouldn't we need some kind of server-specific Client ID in DAVx5 to make that a safe "generic" authentication? I'm also not sure if OAuth2 is working the same on all implementations. Maybe @rfc2822 knows more, since they implemented this in DAVx5.