LDAP Synchronization with Local Users

How would I go about regularly copying user account data from /etc/passwd on one machine into LDAP?

The situation I’m in is that I’m the sysadmin for an academic computer cluster. We have one master node where all of our users log in to submit jobs and a few dozen compute nodes where the jobs are executed. Users are authenticated locally on the master node and I set up LDAP for authentication on the nodes.

Right now, whenever I create a user I have to manually copy over their account data to LDAP. The same has to happen whenever a user changes their password or has group membership change. I’d like to create a cronjob to automate this for me. Given that this feels like a sort of common sysadmin task I’d expect that there is a script already existing that will do this. However, I haven’t found anything in my searches. Additionally, I realized that running an ldapmodify command requires authentication and so it can’t just be run in cron. How do people get around this in their systems?