How to redirect users to new IP

A service (Database)we use on the I'net authenticates us by a range of
IP addresses we have provided them. Let's say 200.200.200.1-10

Some of our users have a different ISP and therefore show a different
IP when trying to log in to the Database.
A while back, I created a password protected site on our web server
which, when you logged in to it from outside of our WAN, redirected you
to the Database log in page, and it looked to the Database service like
the request was coming from our WANs range of IP addresses.

That web server crashed a couple months ago and I lost those web pages
and configuration, and I can't remember how I did it.

Anyone have a clue how I might do this again?