title: System.Net.Http.HttpClient adding If-Modified-Since header
body: <p>I am attempting to issue an Http Get request from a windows universal app and seeing an odd behavior. (not sure if the fact that it is a universal app is related or not).</p>
  
  <p>The simplified code in question is this:</p>
  
  <pre><code>var client = new HttpClient();
  var response = await client.GetAsync("https://storage.googleapis.com/pictureframe/settings.json");
  var s = await response.Content.ReadAsStringAsync();
  </code></pre>
  
  <p>In a unit test or console app that works as expected and the variable <code>s</code> contains the json content.</p>
  
  <p>However in the app where I am trying to add that code (Universal Windows App targeting Windows 10 build 10240) the raw http request looks like this:</p>
  
  <pre><code>GET https://storage.googleapis.com/pictureframe/settings.json HTTP/1.1
  Host: storage.googleapis.com
  If-Modified-Since: Sun, 27 Dec 2015 18:00:08 GMT
  If-None-Match: "5c43f7f07270bda3b7273f1ea1d6eaf7"
  Connection: Keep-Alive
  </code></pre>
  
  <p>The <code>If-Modified-Since</code> header rightly causes google to return <code>304 - not modified</code> so I get no json file back. The thing is I am not adding that header, nor can I figure out where it is being added and how to stop it.</p>
  
  <p>Is there a circumstance in which this would be expected and if so how does one control that behavior.</p>