title: HttpRequestMessage with Windows Authentication
body: <p>I'm trying to do some integration testing on an ASP.Net Core app with Windows Authentication enabled. For controller methods with the [Authorize] attribute I need to send through the current windows identity in the request.</p>
  
  <p>There is lots of information on how to do this using the old HttpWebRequest method, but I can find no information on doing this through HttpRequestMessage. Presumably I have to encode and send through the current user in the authentication header? Can anyone help?</p>