private async void refreshUsers() {
     HavissIoTCommandBuilder commandBuilder =new HavissIoTCommandBuilder();
     commandBuilder.getUsers();
     if (Config.username.Length > 0)
     {
         if (Config.password.Length > 0)
         {
             commandBuilder.addUser(Config.username, Config.password);
         }
         else
         {
             commandBuilder.addUser(Config.username);
         }
     }
     string response = await SharedVariables.client.request(commandBuilder.getJsonString());
     JObject jsonObject = null;
     JArray jsonArray = null;
     try
     {
         jsonObject = JObject.Parse(response);
         jsonArray = (JArray)jsonObject.GetValue("r");
     }
     catch (Exception ex)
     {
         MessageDialog message = new MessageDialog(ex.Message, "Request parse error");
         return;
     }
     List<string> usernames = new List<string>();
     SharedVariables.userHandler.clearUsers();
     foreach (JObject j in jsonArray)
     {
         try
         {
             string username = (string)j.GetValue("name");
             bool OP = (bool)j.GetValue("isOP");
             bool isProtected = (bool)j.GetValue("isProtected");
             bool isPasswordProtected = (bool)j.GetValue("isPasswordProtected");
             User user = new User(username, OP, isProtected, isPasswordProtected);
             SharedVariables.userHandler.addUser(user);
             usernames.Add(username);
         }
         catch (Exception ex)
         {
             MessageDialog message = new MessageDialog(ex.Message, "Request parse error");
             return;
         }
     }
     available_users.ItemsSource = usernames;
 }