I\'m using webbrowser control to login any site. And then i want to download some sub page html using WebRequest (or WebClient). This links must requires authentication.
If you can retrieve the necessary cookies from the WebBrowser control after they are set by the site you are logging into, you should be able to use those same cookies with WebRequest/WebClient.
This article outlines how to use cookies with a WebClient; you have to subclass it, but it's only a single override that's needed.