This idea has been merged into another idea. To comment or vote on this idea, please visit PL-I-197 Login with multi-factor authentication.
This would make it possible to add multi-factor authentication (MFA) to the backoffice login.
Maybe look at this for inspiration, if you would make it possible to set the url backoffice redirects to when not authenticated.
https://forum.litium.com/t/override-backoffice-bo-login/1965