Web View (Windows Authentication Problem)

Hi,

  Scenario:
           I need to access to our clients website and there website is using Windows authentication from the server (IIS).  So, once you go to there website. It will prompt for  a username and password in the browser.   

          When I use a regular browser such as Safari, chrome or IE from the desktop. They will display the authentication window and I can type the username and password and put a check mark for remembering the password.


 Problem:
         When I use this code below, It will not display the Windows Authentication window.  In android device, it will display right away "401-Unauthorized: Access is  denied due to invalid credentials".

          In IPhone device, it's NOT  displaying anything. NO Authentication window show up. And just only a blank page.

Question:
How do I pass a parameter for the Authentication Window? or How do I display the Windows Authentication window inside the Web View?

 Here's the code below that I'm using and this code can't display the windows authentication window:

  var browser = new WebView ();
        browser.Source = "http://www.MyClientRestrictedwebsite.com"; 
        Content =browser;

Please help...

Thanks