I don’t know whether the free version of Nginx has a Relying Party Implementation, but I have used this plugin for Apache2 and OIDC in the past: https://github.com/OpenIDC/mod_auth_openidc

This page might have something, but I can’t read it myself on mobile cause it shows up broken: https://openid.net/certification/certified-openid-relying-pa...

I know it’s not just OAuth but OIDC had a pretty decent provider support and I could even self-host a Keycloak instance - it was annoying to setup but worked okay in practice, could define my own users and then just get a decent login page when needed and otherwise just got into the sites I wanted.

Personally though, it felt a bit overkill when compared to basicauth for anything not run in public or for a lot of users.