public User GetCurrentlyLoggedUser()
        {
            var user = new User {DisplayName = "guest_" + rand.Next(1000), Id = Guid.NewGuid().ToString()};
            user.ThumbnailUrl = string.Format("http://www.gravatar.com/avatar/{0}.jpg?s=30&d=monsterid", 
                System.Web.Security.FormsAuthentication.HashPasswordForStoringInConfigFile(user.Id, "md5")).ToLower();
            if (!users.ContainsKey(user.Id)) users.Add(user.Id, user);

            Debug.WriteLine("GetCurrentlyLoggedUser() called; returned user " + user.Id + " " + user.DisplayName);

            return user;
        }
        public ChatRequest UpdateMessengerPresence(HttpContext context, User user)
        {
            messengerProvider.UpdateLastOnline(user.Id);

            ChatRequest request = messengerProvider.GetChatRequest(user.Id);

            if (request != null)
            {
                request.ChatRequestMessage = String.Format("User <b>{0}</b> wants to chat with you!",
                                                           request.FromUsername);
            }

            return request;
        }