title: HTTPClient to simulate form submission on ASPX - Invalid viewstate
body: <p>I am trying to simulate a form submission on an ASPX.NET site.</p>
  
  <p>The flow of the website when accessed in a browser is as follows:</p>
  
  <p>1) In a browser the user visits <a href="http://mysite.com/" rel="nofollow">http://mysite.com/</a> which is configured with Basic Authentication</p>
  
  <p>2) Upon correct credentials, the user is shown a form with one input text box and a button (URL stays <a href="http://mysite.com/" rel="nofollow">http://mysite.com/</a> but the form being served is Default.aspx)</p>
  
  <p>3)User enters some text and presses submit... </p>
  
  <p>4) The page reloads... URL is still <a href="http://mysite.com/" rel="nofollow">http://mysite.com/</a>... but there is a timer which triggers after 10 secs and downloads a file from <a href="http://mysite.com/Downloader" rel="nofollow">http://mysite.com/Downloader</a></p>
  
  <p>I am trying to simulate this flow in my program using HTTPClient.</p>
  
  <p>1) Do a GET on <a href="http://mysite.com" rel="nofollow">http://mysite.com</a></p>
  
  <p>2) Extract hidden form fields __EVENTVALIDATION and __VIEWSTATE</p>
  
  <p>3) Create a POST request with above two and other form fields and POST it to <a href="http://mysite.com" rel="nofollow">http://mysite.com</a> RESULTS in Invalid Viewstate exception.</p>
  
  <p>How do I achieve this in HTTPClient?</p>