How to bind PasswordBox with wpf in MVVM

<pre>public class BoundPasswordBox
    {
        public static readonly DependencyProperty PasswordProperty = DependencyProperty.RegisterAttached("Password", typeof(string), typeof(BoundPasswordBox),
            new FrameworkPropertyMetadata(string.Empty, OnPasswordPropertyChanged));

        public static readonly DependencyProperty AttachProperty =DependencyProperty.RegisterAttached("Attach",typeof(bool), typeof(BoundPasswordBox), 
            new PropertyMetadata(false, Attach));

        private static readonly DependencyProperty IsUpdatingProperty =DependencyProperty.RegisterAttached("IsUpdating", typeof(bool),
           typeof(BoundPasswordBox));


        public static void SetAttach(DependencyObject dp, bool value)
        {
            dp.SetValue(AttachProperty, value);
        }

        public static bool GetAttach(DependencyObject dp)
        {
            return (bool)dp.GetValue(AttachProperty);
        }

        public static string GetPassword(DependencyObject dp)
        {
            return (string)dp.GetValue(PasswordProperty);
        }

        public static void SetPassword(DependencyObject dp, string value)
        {
            dp.SetValue(PasswordProperty, value);
        }

        private static bool GetIsUpdating(DependencyObject dp)
        {
            return (bool)dp.GetValue(IsUpdatingProperty);
        }

        private static void SetIsUpdating(DependencyObject dp, bool value)
        {
            dp.SetValue(IsUpdatingProperty, value);
        }

        private static void OnPasswordPropertyChanged(DependencyObject sender,DependencyPropertyChangedEventArgs e)
        {
            PasswordBox passwordBox = sender as PasswordBox;
            passwordBox.PasswordChanged -= PasswordChanged;

            if (!(bool)GetIsUpdating(passwordBox))
            {
                passwordBox.Password = (string)e.NewValue;
            }
            passwordBox.PasswordChanged += PasswordChanged;
        }

        private static void Attach(DependencyObject sender,DependencyPropertyChangedEventArgs e)
        {
            PasswordBox passwordBox = sender as PasswordBox;

            if (passwordBox == null)
                return;

            if ((bool)e.OldValue)
            {
                passwordBox.PasswordChanged -= PasswordChanged;
            }

            if ((bool)e.NewValue)
            {
                passwordBox.PasswordChanged += PasswordChanged;
            }
        }

        private static void PasswordChanged(object sender, RoutedEventArgs e)
        {
            PasswordBox passwordBox = sender as PasswordBox;
            SetIsUpdating(passwordBox, true);
            SetPassword(passwordBox, passwordBox.Password);
            SetIsUpdating(passwordBox, false);
        }

    }

<passwordbox x:name="TxtPassword" util:boundpasswordbox.attach="True" util:boundpasswordbox.password="{Binding Path=Password,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged,ValidatesOnDataErrors=True,NotifyOnValidationError=True}" xmlns:util="#unknown" xmlns:x="#unknown">
</passwordbox>

xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"

<PasswordBox Grid.Column="1" PasswordChar="*" x:Name="pwbox"     Password="test"   >
                      <i:Interaction.Triggers>
                          <i:EventTrigger EventName="PasswordChanged" >
                              <i:InvokeCommandAction Command="{Binding PasswordChangedCommand }"  CommandParameter="{Binding ElementName=pwbox,  Mode=OneWay}"/>
                          </i:EventTrigger>
                      </i:Interaction.Triggers>
                  </PasswordBox>

public ICommand PasswordChangedCommand
    {
        get
        {
            return new RelayCommand<object>(ExecChangePassword);
        }
    }

  

    private void ExecChangePassword(object obj)
    {
        yourPassword = ((System.Windows.Controls.PasswordBox)obj).Password;
    }

public class RelayCommand<T> : ICommand
{

 
 
    /// <param name="execute">The execution logic.</param>
    public RelayCommand(Action<T> execute)
        : this(execute, null)
    {
    }
      public void Execute(Object parameter)
        {
            _execute((T)parameter);
        }}

<passwordbox name="password" />
<button>
<interactivity:interaction.triggers xmlns:interactivity="#unknown">
<interactivity:eventtrigger eventname="Click">
<cmd:eventtocommand command="{Binding SignIn}" commandparameter="{Binding ElementName=password}" xmlns:cmd="#unknown" />
</interactivity:eventtrigger>
</interactivity:interaction.triggers>
</button>
/*
xmlns:interactivity="http://schemas.microsoft.com/expression/2010/interactivity"
xmlns:cmd="clr-namespace:GalaSoft.MvvmLight.Command;assembly=GalaSoft.MvvmLight.Extras.WPF4"
*/

private void SigningIn(object parameter)
{
PasswordBox PasswordObj= parameter as PasswordBox;
string Password = password.Password;//here is the entered password
}

<PasswordBox x:Name="txtPassword" Margin="0,10" materialDesign:HintAssist.Hint="Password" Style="{StaticResource MaterialDesignFloatingHintPasswordBox}" FontFamily="Champagne & Limousines" FontSize="18" PasswordChanged="txtPassword_PasswordChanged">
                        <PasswordBox.DataContext>
                            <Binding Path="Password" UpdateSourceTrigger="PropertyChanged">
                                <Binding.ValidationRules>
                                    <demo:NotEmptyValidationRule ValidatesOnTargetUpdated="True" />
                                </Binding.ValidationRules>
                            </Binding>
                        </PasswordBox.DataContext>
                    </PasswordBox>

private void txtPassword_PasswordChanged(object sender, RoutedEventArgs e)
       {

           loginViewModel.Password = txtPassword.Password;
           loginViewModel.UserName = txtUserName.Text;
           DataContext = loginViewModel;
       }

public class LoginViewModel : INotifyPropertyChanged
  {
      private string _UserName;
      private string _Password;
      public LoginViewModel()
      {
          LongListToTestComboVirtualization = new List<int>(Enumerable.Range(0, 1000));
      }
      public string UserName
      {
          get { return _UserName; }
          set
          {
              this.MutateVerbose(ref _UserName, value, RaisePropertyChanged());
          }
      }
      public string Password
      {
          get { return _Password; }
          set
          {
              this.MutateVerbose(ref _Password, value, RaisePropertyChanged());
          }
      }

      public IList<int> LongListToTestComboVirtualization { get; }

      public DemoItem DemoItem => new DemoItem("Mr. Test", null, Enumerable.Empty<DocumentationLink>());

      public event PropertyChangedEventHandler PropertyChanged;

      private Action<PropertyChangedEventArgs> RaisePropertyChanged()
      {
          return args => PropertyChanged?.Invoke(this, args);
      }
  }

public class NotEmptyValidationRule : ValidationRule
    {
        public override ValidationResult Validate(object value, CultureInfo cultureInfo)
        {
            return string.IsNullOrWhiteSpace((value ?? "").ToString())
                ? new ValidationResult(false, "Field is required.")
                : ValidationResult.ValidResult;
            
        }
    }