title: HttpResponseMessage missing headers while using HttpClient but fiddler finds it
body: <p>I am making a simple <code>HttpClient</code> call like this:</p>
  
  <pre><code>Uri basePath = new Uri("https://my-host.com/");
  string path = "api/my-path";
  
  using (HttpClient httpClient = new HttpClient())
  {
      httpClient.BaseAddress = basePath;
  
      HttpResponseMessage response = await httpClient.GetAsync(path);
      if (response.IsSuccessStatusCode)
      {
          response.Headers.Select(header =&gt; header.Key).Dump();
      }
  }
  </code></pre>
  
  <p>I am looking for a custom auth-header on the response but it is missing when I iterate over <code>Headers</code> collection.</p>
  
  <p>However, same Http request caught by <code>Fiddler</code> shows the header.
  If I make same request on <code>Postman</code> or any browser, I see the header.</p>
  
  <p>Wondering what am I missing here.</p>
  
  <p>[Update]</p>
  
  <p>Raw Headers captured on <code>Fiddler</code> by executing same code above:</p>
  
  <pre><code>HTTP/1.1 302 Found
  Cache-Control: no-cache
  Pragma: no-cache
  Expires: -1
  Location: &lt;redacted&gt;
  Server: Microsoft-IIS/8.0
  WWW-Authenticate-Test: &lt;redacted&gt;
  X-AspNet-Version: 4.0.30319
  Set-Cookie: &lt;redacted&gt;
  X-UA-Compatible: IE=edge
  Date: Sat, 11 Nov 2017 23:15:19 GMT
  Content-Length: 0
  </code></pre>
  
  <p>Headers printed by above code:</p>
  
  <pre><code>Pragma 
  Strict-Transport-Security 
  X-Content-Type-Options 
  X-Frame-Options 
  x-ms-request-id 
  Cache-Control 
  P3P 
  Set-Cookie 
  Server 
  X-Powered-By 
  Date
  </code></pre>
  
  <p>I would like to capture the header <code>WWW-Authenticate-Test</code> which is somehow filtered out while it goes through the <code>HttpClient</code> magic.</p>