I did something similar at work on our intranet server. We have hundreds of people who access our site and my office was strictly against remembering usernames and passwords for the admin side of our site, so what i did was created a table called authorized and listed ip addresses of computers that had authorization to use the administration side of our intranet site. Then I did something similar to this below on a global variables form (we use fuseactions so this was called on every page):
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