private void ExecuteLoginCommand(object obj)
        {
            var username = loginViewModel.Username;
            var password = loginViewModel.Password;

            user = socket.CanUserLogin(username, password);
            //user = new User() {
            //   Username = "******", Firstname = "paul", Lastname= "Finkbeiner", IsAdmin = true, Id = 0, Version = 0
            //};
            if (user != null)
            {
                loginWindow.DialogResult = true;
                loginWindow.Close();
            }
            else
            {
                MessageBox.Show("Login fehlgeschlagen");
            }
        }