The authentication is based on Kerberos5 and not on the userPassword LDAP attribute. The easier solution is to use the cpw script to set the password. For example to set the fulvio’s password to “fulviopassword” use the following command:
/root/kerbynet.cgi/scripts/cpw fulvio “” “fulviopassword” NOCHECKPW
Now, you just have to write a script that automatically extracts usernames and passwords from the LDIF file and calls the cpw command.