DerFrie Is there a chance to get this added to the "official" code?
What do you mean by "official"? This extension is not official. One can always make another extension that adds its own provider.
A general statement (see FriendsOfFlarum/oauth#19) -
I don't know how many providers we'll add into this extension because that means we'll need to mantain them all - and things like nextcloud would require we maintain that and have instances to test it. We had a PR for WeChat that we closed because we cannot test it - a separate extension can easily hook into this one or Flarum directly and add that.
Not all providers need to be in this ext, we just have multiple ones here because we can test them all and are able to update them easily.