There can be many reasons why a request is not allowed or authorized. 403 and 405 HTTP error codes do not prompt the visitor for credentials. Only 401 and 407 responses are credentials prompts. Only raise a username and password request when facing a 401 or 407. Fixes: https://gitlab.gnome.org/GNOME/gnome-calendar/-/issues/645 Fixes: https://gitlab.gnome.org/GNOME/gnome-calendar/-/issues/552