Single Signon in PHP

[rlarner]

Sorry if this is a duplicate post, but I am new to vB and haven't been able to find an answer to this. We have an existing site in PHP that has it's own registration and login. I'd like to make it so that when a customer who is logged in to the site navigates to the forums they are already logged in and can post.

Also, someone who goes directly to the forums should be able to view existing threads, but if they try to respond they should be redirected to login to the site via our existing (no vB) login screen.

Thanks in advance for the help!