ServiceAccountViewModel.cs

namespace ServicesTool2.ViewModel
{
    using System;
    using System.DirectoryServices.AccountManagement;
    using System.Windows;
    using System.Windows.Controls;
    using System.Windows.Input;

    using GalaSoft.MvvmLight;
    using GalaSoft.MvvmLight.CommandWpf;

    public class ServiceAccountViewModel : ViewModelBase
    {
        public ServiceAccountViewModel()
        {
            Domain = Environment.UserDomainName;
        }

        public string Domain { get; set; }

        public string Username { get; set; }

        public ICommand VerifyCommand => new RelayCommand<object>(Verify);

        private async Task Verify(object parameter)
        {
            var passwordBox = parameter as PasswordBox;
            if (passwordBox != null) {
                string password = passwordBox.Password;
                try {
                    using (var pc = new PrincipalContext(ContextType.Domain, Domain)) {
                        bool isValid = await Task<bool>.Factory.StartNew(() => pc.ValidateCredentials(Username, password));

                        MessageBox.Show(isValid ? "success" : "failure");
                    }
                } catch (Exception ex) {
                    MessageBox.Show(ex.Message);
                }
            }
        }
    }
}