[Zope] LDAPUserFolder at Zope root

Hello, this might be trivial but I just can't find a way to do it. How does one replace the initial UserFolder at Zope root with a LDAPUSerFolder ? I tried the dummy way : delete the acl_users with an intent to instanciate a LDAPUSerFolder afterwards but that locked me out in a way I could do nothing but recreate a new Zope instance... skip-authentication-checking in etc/zope.conf didn't help... Zope 2.7 debian testing package. Oscar