🎉
So I was tinkering with matrix (the chat protocol) a lot lately and finally got what I wanted to have for a long time: Nextcloud with Matrix.
Nextcloud is providing OAuth2 to Matrix-Synapse, both run on separate subdomains since the NC Element app is an iFrame which prevents OAuth logins.
I have written down a full documentation so you can set this up too 📖
... but here is the next challenge I face: set up a blog (again).