With #3619 we are attempting to switch to Django's authentication backend system for logging in users.

While there exists a ready-made library (see django-auth-ldap) it would take longer to adapt it to NAV's ancient idiosyncracies than reusing the existing ldap integration and "just" writing a Django-style auth backend. (Also we won't need to change any settings...)

The POC needs to branch off #3619, not master!

Necessary functions to reuse are found in nav.web.auth.

Spec:

Assuming that the ldap-backend comes first in the list of backends:

1. On login (implementation of BaseBackend.authenticate):
   • If ldap is not available, return None
   • If the user does not exist in ldap, return None
   • if the user exists in ldap but not locally, create the user locally and set the inputted password as the password for the new user.
2. Try authenticating the user in ldap.
   • If the user is newly created and the inputted password is wrong, set the locally stored password to invalid and return False
   • Return False for any other errors
   • If everything ok, update premissions the NAV way (nav.web.auth._handle_ldap_admin_status) and return the Account