Staff can login as superuser

[Albyorix]

This package is great work, thanks !

I've tested it for my app, and because I need any of my staff to login as a user, I added the login callback:
SU_LOGIN_CALLBACK = "example.utils.su_login_callback"

The problem is that now, any staff can login as superuser and edit their own permissions...

How can I restrict the login as to non-staff user only ?

Thanks