Optional function for using a third-party authentication system with Supabase. The function should return an access token or ID token (JWT) by obtaining it from the third-party auth client library. Note that this function may be called concurrently and many times. Use memoization and locking techniques if this is not supported by the client libraries.
When set, the auth
namespace of the Supabase client cannot be used.
Create another client if you wish to use Supabase Auth and third-party
authentications concurrently in the same application.