How to make 2 websites share one url

I know there is a script but cannot remember the script. I have one page on my primary website, which is a login page for clients that I want to use for another website also. The problem is, I want the url at the top to say the url that the client logs in at on the secondary website so that way they never know that they are actually logging in to the primary website that I am wanting to share the same sql databse for both websites but not the same primary url. I keep trying to do it and everything looks find until they actually login, as soon as they login the secondary url turns in to the primary url giving it away.

You can use frames.

Yes that would work if you are wanting to share one sql

Using "frames" is one way, although the status bar of the browser might reveal the first domain's path while loading your page(s).

If you have access to Apache's configuration file, you could set the "DocumentRoot" directive to share the www folder of the first domain with your second domain. That ways, you have only one set of files in the first domain's www area, while at the same time you're also running the second domain but merely serving files off the www area of the first domain.

Hope this helps!