Accessing webpages only through a portal

I am trying to design a web application portal for the company i work for. We have all of these web apps scattered about, and I have the portal up and running, but I want to make it so people can access the apps ONLY BY GOING THROUGH THE PORTAL. So they can't just favorite the site and go to /myserver/myapp/index.aspx i want them to have to get through it by using the portal. Any suggestions? I thought of making a cookie but for each app, but that would take some time to modify all the code. Is there a easy way to do that in IIS or Visual Studio.net? Thanks

You will need some kind of authentication system to prevent users from going directly to a url. You could use windows permissions, or products like authentix.

This depends of the architecture of your portal and of applications that you were talking about.HTTP authetication can be the solution of your problem, but only if this isn'g gonna stop your portal in accessing those apps. So, you can try to protect one of your apps and if your portal still shows this application, then, everything's ok. As for the way of the protection, you can use windows permissions or a free tool, IISPassword..
GreetingZ

Thanks for the suggestions guys. Based on the deployment and structure of the portal, I ended up placing a cookie on the last page of the portal that all applications check for. It seems to be working great.. .knock on wood