Subset of users tied to specific machine/browser?

[rtkluttz]

I need a way to authenticate a subset of my users to a specific PC and specific web browser. We have to use some shared accounts where there is high personnel turnover and we can't be changing passwords every time someone new comes and goes, and we don't want these shared accounts to be used from these users homes or mobile devices. So we need to use user certs or any other method that will allow browser access to a specific zimbra user account without having to type a username and password but keep it boxed in to a single physical location and browser.

Any ideas on how I can accomplish this?