How to manage Security on web pages of .NET

I have a web system which is control from the url of pages like:

http://localhost/web/dlg/main.aspx?knd=in&Int=252&pID=-1&pLnk=-1&Lkp=false&parent=&systemInterface=true&ID=5

But there is a security problem because some of users has few permissions of pages and others dont have permissions, Also users can change the parameters of URL and access forbidden pages, so how can i control this, something like a token in URL?

Someone has a start for me about what can i search for?