public UserModel Index(string id)
        {
            //authorize user
            //TODO authorize

            // get + map data
            var user = _backend.GetUser(id);

            if (user == null)
            {
                throw new HttpResponseException(new HttpResponseMessage(HttpStatusCode.NotFound)
                {
                    Content = new StringContent(String.Format("'{0}' does not match a user in this system", id))
                });
            }
            else
            {
                return(new UserModel(user));
            }
        }