appwrite/docs/references/account/create-session-oauth2.md

Allow the user to login to their account using the OAuth2 provider of their choice. Each OAuth2 provider should be enabled from the Appwrite console first. Use the success and failure arguments to provide a redirect URL's back to your app when login is completed.

If there is already an active session, the new session will be attached to the logged-in account. If there are no active sessions, the server will attempt to look for a user with the same email address as the email received from the OAuth2 provider and attach the new session to the existing user. If no matching user is found - the server will create a new user..