Need to restrict access to modify contact list

Hi, all,

I'm trying to configure an XMPP server where each user is already assigned a username/password and is allowed access from any client. While it is on an open network accessible from anywhere on the world wide web, I would like to have each user's contact list maintained only by an admin. In other words, each individual user is not allowed to add or remove another user from their predefined contact list, and they are unable to even contact other users outside of their contact list.

I see that most jabber servers allow you to configure your server so that you can assign users groups and their own lists, but still allow them to modify their assigned list. Is there any plugin or feature available in ejabberd (or any other XMPP server for that matter) which allows one to prescribe unmodifiable lists?

Thanks in advance.