Visitor Access options for un-supported OAuth provider

What are the options for Visitor Access with an un-supported OAuth provider.

The answer to that question depends on what your goals are. If you just want to use a client side library that connects to a service like Okta, Firebase Authenticatoin, AWS Cognito, Auth0, then you can use those and any other client side auth you want. With Identity you can only use our support auth providers.