Access check based on different server

Hi ya'all

I surely hope that someone can help me out with this rather (for me) challenging task I’m facing:

I have 'Gallery' running on a LAN that includes several servers that have each of their own permission configuration. ‘Gallery’ is running on a simple WinXP with FoxServ, and it’s doing a great job – but now I need to control the user access, based on the configuration of another server (that can’t be setup to run ‘Gallery’).
My first idea was simply to put the images on the access controlled server, and link to them from ‘Gallery’, but I learned from the Gallery-FAQ, that it is not possible (and it would do my job, running the gallery very complex – so never mind that). My next idea is to put some lines of code into the index file (or another file that is included every time a gallery album is called from the client), that points to a file, located on the access controlled server. See: “client can’t get the file = redirected to another site/ client can get the file = gallery continues as if nothing ever happened.
The problem here is, that the server running ‘Gallery’ DO always have access to this server, so the returned information has to be based on the clients access permission.

Since I’m not into any PHP codes, I happily believe that this can be done – I just don’t know how. Can anyone give me a hint please?