Connect existing OCIS instance to Google OAuth OIDC

Hello,

I have an existing OCIS 5.0.8 instance running in docker. There are a few existing users with files. The instance is using built-in OIDC. I’m really new to OIDC. I would like to use Google OAuth2, which I think is an OIDC. Is there a tutorial / guide? I can not find one after searching here, on GitHub issue and on Internet. I do find guides for keycloak, authentik and Authelia. As I understand, they are a kind of gateway and can “forward” authentication to multiple sites such as Google, GitHub and etc. However, I would like to, if possible, avoid adding another software if possible.

Suppose it is possible to use Google as OIDC directly, would the mapping existing users be automatic? My users are using their @gmail.com addresses as user names.

Thanks!