Hello, why are the supabase auth discord scope guilds data of the user not exist in session?

They should be in the session right after after a user signsup or in with signInWithOAuth. They are only available on that initial session. You have to deal with storing them if you want. Supabase does not keep them around for security. https://supabase.com/docs/guides/auth/social-login#provider-tokens