Document the metadata received from OAuth providers

[MiloWatson]

Improve documentation

Link

https://supabase.com/docs/guides/auth#providers

Describe the problem

Currently there is no documentation surrounding the metadata that is received and stored in the auth.users raw_user_meta_data column when a user signs up via a third party auth provider. This makes it complicated to know if a specific auth provider returns the data fields that are required for applications, for example, I am requiring a username on signup and have made a public.users table that contains a not null field for the username, but Google OAuth2 does not return a username in metadata and therefore the user sign up fails.

The only way to know what metadata is currently provided by each is to remove all constraints and sign in with each provider and then review the auth.users table information.

Describe the improvement

A page showing the metadata returned by each auth provider.