Security - automatic login to a directory protected by .htaccess - how

[scotch33]

I have a script where the following happens...

A visitor arrives from a third party site via a hidden form(i.e. nothing to fill in, just looks like a normal link).  In the form the visitor's username and password from the third party site are sent as variables.  Upon arrival at my site they are asked to re-input theur user name and password and if they match the variables sent they are going to be allowed into a members area.  If not they are redirected to the public area.

This i can do, what i need to research is how to include the user name and password to my members area in the script so it automatically logs in members without presenting them with more boxes to fill in.  Can anyone point me in the right direction for a tutorial or explanation about how i can make a php page automatically log in to a secured directory, and how to keep that php page hidden?

Thanks!

[hopeless]

Could you drop the htaccess log in? I wouldn't know any way of filling in the htaccess form but I'd probably use an authorisation system whereby each page rather than the directory is protected using code and viewable only to approved users. They then get approved or otherwise on the landing page.