Simple auth solutions

Are there any simple auth solutions like firebase auth that can be used on F-Droid? I mainly want to be able to authenticate users in cloud functions, only for user stats sharing feature for now and with potentially monetized features in future.

I can’t find anything at the moment except of writing account management system on my own, and I’m not very familiar with back-end development, it seems complicated with emails, 2FA and other things. I also consider investigating if it’s possible to open my custom firebase login web-page in system’s web browser just to retrieve auth token or something, if it’s considered acceptable for f-droid

are the libs and code open source?

Looks like no according to this Github Issue, that’s why I’m talking about using a website to login so that no libs are added to the app, as far as I understand it will make my app marked as NonFreeNetwork but it’s still acceptable

Yes, oauth things via the browser are acceptable