title: Authorization code grant type for service to service communication
body: <p>I have two services: Service A and Service B</p>
  <p>I have a central Identity Server that issues and validates tokens.</p>
  <p>I need some of the resources of Service B to be accessed only by Service A.</p>
  <ol>
  <li>How do I validate the audience, or how do I make sure that for ex.
  the client credentials token of Service A is valid when calling
  Service B, and tokens from other services are invalid.</li>
  <li>Is it a bad practice or are there any issues in using authorization
  code grant type for service to service authorization ?</li>
  </ol>