Hi David,
My apologies for the late response. This is in-fact possible using the session variable User - IP Address.
The simplest way that I can think of for you to accomplish this would be using the OnScreenLoad event on the user’s home screen. You would need to retrieve the user’s IP address within this event. Then use a conditional statement to “authenticate” the user and hide all tab links using several Show/Hide Tab Link actions within the conditional statement if authentication fails. Hiding the tab links will revoke access to the screens they link to.
I hope this helps.
--Audisho