anchor.diff:      fun (ctx : HttpHandlerContext) ->
           let user = ctx.HttpContext.User
           if user.IsInRole role
  -        then async.Return (Some ctx)
  +        then
  +            logDebug ctx "passed role requirement"
  +            async.Return (Some ctx)
           else authFailedHandler ctx
   
   /// Validates if a user has at least one of the specified roles.
  
positive.code:         |> Seq.map    (fun h -> h.ToString())
          |> Seq.exists (fun h -> mimeTypes |> Seq.contains h)
          |> function
              | true  -> Some ctx
              | false -> None
              |> async.Return          
  
  /// Challenges the client to authenticate with a given authentication scheme.
  let challenge (authScheme : string) =
  
negative.code:     fun (ctx : HttpHandlerContext) ->
          async {
              match handlers with
              | []              -> return None
              | handler :: tail ->
                  let! result = handler ctx
                  match result with
                  | Some c -> return Some c
                  | None   -> return! choose tail ctx
          }
  
  /// Filters an incoming HTTP request based on the HTTP verb
  