title: AD FS client authentication from a web-api app. How to?
body: <p>Given user credentials (i.e. username, password), I'd like to authenticate the user from within our web-api applictation.</p>
  
  <p>I'm considering using a class derived from Attribute and IAuthenticationFilter.  The class will use HttpClient to connect to an AD FS server, submit user credentials and retrieve resulting tokens. Selected methods within ApiController(s) will be decorated with the above attribute.</p>
  
  <p>Will the above work?<br>
  What is a uri format that needs to be sent to the ADFS server?
  Does the http request sent to the server need a body/payload?
  What is a response format from the server in case of success (with token)/failure?</p>
  
  <p>I'd appreciate any examples and pointers to on-line docs.</p>
  
  <p>Thanks.</p>