Hi there and sorry to be slow to get back to you.
I think that the final answer will depend on how you are using OAuth - for instance with Identity (Authenticate users with Netlify Identity | Netlify Docs) the backing authentication service is gotrue (GitHub - netlify/gotrue: An SWT based API for managing users and issuing SWT tokens) which our running instance of does not support any additional authentication services for, at present. However as you can see that is an open source service you could fork and run your own copy of and augment in any way you like (such as Feature Request: Please support goth auth providers · Issue #122 · netlify/gotrue · GitHub).
To respond to your additional questions in Netlify Identity integrating with Keycloak identity provider which are clearly about identity:
- no - no way to add additional auth providers that our service will support
- it depends (well, obviously you can’t choose your own provider) but you can either limit the auth providers in the Identity settings OR (this is a non-exclusive OR ;)) you can choose to modify the identity widget you would likely use (GitHub - netlify/netlify-identity-widget: A zero config, framework free Netlify Identity widget) to process signups and logins to limit what it shows.
If I guessed wrong and you aren’t talking about using OAuth with Identity, could you let me know some more details about how you are trying to use it?