We only need to know which url the user is visiting. Therefor, we need a proxy script which rewrites all the 'h ref' urls on the displayed page to something like:
[url removed, login to view]://[url removed, login to view]
so that the proxy script can display this page for them.
Most proxies also rewrite the urls for images, audio, movies, etc. We don't need all of that. We do however need to have forms work on the pages which are proxied.