In order to compare what you do in code, and what the browser does, I am sure a HTTP debugging tool such as Fiddler, would be the easiest solution.
Fiddler acts as a proxy between client and server, and displays all information sent over the HTTP protocol.
It is possible that you will need to configure your .NET app to use the proxy that Fiddler provides. This blog post provides details on the subject.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…