accessing post data passed through web browser control -winforms

I'm developing a winforms application, in which I have a web browser control, where I have to open certain web page based on the menu item clicked. This is how I'm calling the web page in app

System.Text.UTF8开发者_JAVA百科Encoding encoding =  new System.Text.UTF8Encoding(); 
string postData = "username=xyz";
string header = "";
webBrowser.Navigate(url, "", encoding.GetBytes(postData), header);

How I can access postData values in the webpage?

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If the page at url is also an ASP.Net page, then you can access it by:

String Username = Request.Form("Username");