title: Web API read header value in controller constructor
body: <p>Is it possible to get at the header information in the constructor of a web API controller?  I want to set variables based off a header value but I don't want to have to do it for each method.  I'm particularly interested in a custom header value but I would settle for the Authorization one at this point.  I can get it to work in an <code>AuthorizationFilterAttribute</code> but I also need it at the controller level.</p>
  
  <pre><code>[PolicyAuthorize]
  public class PoliciesController : ApiController
  {
      public PoliciesController()
      {
          var x = HttpContext.Current;  //will be null in constructor
      }
  
      public HttpResponseMessage Get()
      {
          var x = HttpContext.Current;  //will be available but too late
      }
  }
  
  public class PolicyAuthorizeAttribute : AuthorizationFilterAttribute
  {
      public override void OnAuthorization(HttpActionContext actionContext)
      {
          var authHeader = actionContext.Request.Headers.Authorization;  //can get at Authorization header here but no HTTPActionContext in controller
      }
  }
  </code></pre>