M 6 security app only

Steps to reproduce

1. Go th demo author
2. Create a user test@test with role superuser
3. Try to log in with the user > login fail
4. Rename the user to test > login fail again

.. Logs, screenshots, gifs...

Expected results

.. You can create an username with an @ in it, the renamed user can login
Justify non-trivial expectations with a link to a doc or a relevant discussion.

Actual results

User cannot login

Workaround

When current usernames have @ in it, you must use the previous security app.