Session with existing site

I am thinging to use Yii at a site that will be a part of a "portal" but it will be individual as site.

So this site will have a login page.

So can I see if user is already login via the portal login?

So how can I read the session or the cookies of the portal?

The site will be in a subfolder of this portal.

I wish to be understood.

There is an interesting article on about SSO (Single Sign On with PHP and Ajax). There are even some demos. I hope that helps