/etc/cfengine/debian-edu/cf.adduser is in debian-edu-config 1.818+deb8u2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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  debian::
        # The file /etc/adduser.conf control local user creation.
        # For setting up a Debian Edu/Skolelinux server it is recommend
        # to start with a local user on a workstation (that might even be 
        # tjener itself with additional workstation role).
        #
        # For local user creation we want to make sure that local users
        # do not have conflicting uidNumbers, gidNumber with those in LDAP.
        # Patch /etc/adduser.conf
        { /etc/adduser.conf
            # FIRST_UID, LAST_UID for non-LDAP users is 500-999
            ReplaceAll 'FIRST_UID=1000' With 'FIRST_UID=500'
            ReplaceAll 'LAST_UID=29999' With 'LAST_UID=999'
            # FIRST_GID, LAST_GID for non-LDAP groups is 500-999
            ReplaceAll 'FIRST_GID=1000' With 'FIRST_GID=500'
            ReplaceAll 'LAST_GID=29999' With 'LAST_GID=999'
            # local users' homes have permissions 0700
            ReplaceAll 'DIR_MODE=0755' With 'DIR_MODE=0700'
        }
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