title: How do I set a cookie on HttpClient's HttpRequestMessage
body: <p>I am trying to use the web api's <code>HttpClient</code> to do a post to an endpoint that requires login in the form of an HTTP cookie that identifies an account (this is only something that is <code>#ifdef</code>'ed out of the release version). </p>
  
  <p>How do I add a cookie to the <code>HttpRequestMessage</code>?</p>