Disabling users by expiry date

Monday 16 May 2005 2:57:32 am

I have a modified content class called "User" in the Users class group list.

The User class has an attribute "expiry_date" and the idea is that if the expiry date is less than the current date, then the user can't log in and their account is disabled.
I was thinking of using a cronjob to check each day if the users accounts have expired. However i get stuck in trying to understand how to disable the users.
Do i need to change the login kernel files to implement this?
Does anyone know a better way to implement this functionality?

Thanks!