title: web client call server, server call 3rd party, all async?
body: <p>I have a website that is that is architected using an n-layer approach.  The problem I have is that I need the client to make a call to the application layer, one of the other layers will then make a call to another web service somewhere in the world.  The other web service could take some time to come back so what I would like to do, if possible, something along the lines of the following using async requests:
  <img src="https://i.stack.imgur.com/exNhT.png" alt="simple diagram of the async requests"></p>
  
  <p>The client is HTML &amp; JavaScript, the server layers are written in C# (.NET 4.5), the 3rd party web services are just web services I need to consume</p>
  
  <p>How would you go about writing this?
  Any help will be much appreciated</p>