Cisco AAA/Identity/Nac :: ACS 5.2 Adding And Updating Users Automatically

I have a Cisco ACS 5.2 and have set it up as a RADIUS server. I was wondering if there is a way to add and update users automatically? We have a large number of users > 1000 that need to be added into the system and I don't want to do this manually. These users also update their passwords on a regular basis so I would need a script that would update the users automatically without any user intervention.