Unexpected user experience: login attempt becomes a signup

Typically you would expect signing up to be separate from logging in. With this authenticator, we make the login step be the signup step without notifying the user about this being the case or similar.

It would be a significant improvement if we could help users understand this situation better, then we could avoid broken expectations like reported in https://github.com/jupyterhub/the-littlest-jupyterhub/issues/650 for example.

Start by reviewing the authenticator's login flow and the linked JupyterHub issue 650 to understand the reported expectation mismatch. Clarify the intended user-facing behavior and acceptance criteria; the work is done when users are clearly informed that their first login also creates an account.

Written by the indexing model from the issue text.