FACs work on an code-assigned authorization level. All you can do is assign a privilege level to an individual FAC and specify an minimum level on the route pattern. They were not designed to provide authorization on an originating-device basis.
If you need to constrain the ability to dial a pattern to a user (authentication) and have per-user authorization, you can do this by using EM to get a per-user/device authentication to occur and then assigning a line CSS with that user's unique privileges.
