Python 3.9 is now generally available.

google.appengine.api.users.CreateLoginURL

Computes the login URL for redirection.

dest_url String that is the desired final destination URL for the user once login is complete. If dest_url does not specify a host, the host from the current request is used.
federated_identity Decommissioned, don't use. Setting this to a non-None value raises a NotAllowedError

Login URL as a string. The login URL will use Google Accounts.

NotAllowedError If federated_identity is not None.