This requires manually enabling every additional provider.

No, it doesn’t. The docs are confusing on this, but forgejo has two methods to enable oauth/oidc. One is to manually enable them, but there is a second, where people bring their own oauth link.

The docs contain 3 things related to oauth:

• Oauth provider forgejo acts as oauth for someone else
• Ouath client — This is the one where you manually enable providers
• But then there is a third config. Openid. This lets users bring their own openid/oauth link and sign in with that. No manual configuration required on the side of the forgejo server per client.