title: Modify request headers per request C# HttpClient PCL
body: <p>I'm currently using the <a href="https://www.nuget.org/packages/Microsoft.Net.Http">System.Net.Http.HttpClient</a> for cross platform support.</p>
  
  <p>I read that it is not a good practice to instantiate a HttpClient object for each request and that you should reuse it whenever possible.</p>
  
  <p>Now I have a problem while writing a client library for a service. Some API calls need to have a specific header, some MUST not include this specific header.</p>
  
  <p>It seems that I can only manipulate the "DefaultRequestHeaders" which will be send with each request.</p>
  
  <p>Is there an option when actually making the request with e.g. "client.PostAsync()" to modify the headers only for the specific request?</p>
  
  <p>(Info: Requests can be multi threaded).</p>
  
  <p>Thanks in advance!</p>