Add a PasswordBox control.

samples/ControlCatalog/Pages/TextBoxPage.xaml

@@ -14,9 +14,14 @@
                  Watermark="Floating Watermark" 
                  UseFloatingWatermark="True"
                  Text="Lorem ipsum dolor sit amet, consectetur adipiscing elit."/>
+
+        <PasswordBox Width="200"
+                 Watermark="Password Box"
+                 UseFloatingWatermark="True"
+                 Text="Password" />
         <TextBox Width="200" Text="Left aligned text" TextAlignment="Left" />
         <TextBox Width="200" Text="Center aligned text" TextAlignment="Center" />
-        <TextBox Width="200" Text="Right aligned text" TextAlignment="Right" />
+        <TextBox Width="200" Text="Right aligned text" TextAlignment="Right" />        
       </StackPanel>
 
       <StackPanel Orientation="Vertical" Gap="8">

src/Avalonia.Controls/PasswordBox.cs

@@ -0,0 +1,47 @@
+using Avalonia.Controls.Primitives;
+using Avalonia.Styling;
+using System;
+
+namespace Avalonia.Controls
+{
+    public class PasswordBox : TextBox, IStyleable
+    {
+        Type IStyleable.StyleKey => typeof(PasswordBox);
+
+        public PasswordBox()
+        {
+            this.GetObservable(TextProperty).Subscribe(text =>
+            {
+                if (text != null)
+                {
+                    DisplayText = new string(PasswordChar, text.Length);
+                }
+                else
+                {
+                    DisplayText = null;
+                }
+            });
+        }
+
+        public static readonly StyledProperty<char> PasswordCharProperty = AvaloniaProperty.Register<PasswordBox, char>(nameof(PasswordChar), '*');
+
+        public char PasswordChar
+        {
+            get => GetValue(PasswordCharProperty);
+            set => SetValue(PasswordCharProperty, value);
+        }
+
+        public static readonly StyledProperty<string> DisplayTextProperty = AvaloniaProperty.Register<PasswordBox, string>(nameof(DisplayText));
+
+        public string DisplayText
+        {
+            get => GetValue(DisplayTextProperty);
+            set => SetValue(DisplayTextProperty, value);
+        }
+
+        protected override void OnTemplateApplied(TemplateAppliedEventArgs e)
+        {
+            base.OnTemplateApplied(e);
+        }
+    }
+}

src/Avalonia.Themes.Default/PasswordBox.xaml

@@ -0,0 +1,64 @@
+<Styles xmlns="https://github.com/avaloniaui" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+  <Style Selector="PasswordBox">
+    <Setter Property="Background" Value="{DynamicResource ThemeBackgroundBrush}"/>
+    <Setter Property="BorderBrush" Value="{DynamicResource ThemeBorderMidBrush}"/>
+    <Setter Property="BorderThickness" Value="{DynamicResource ThemeBorderThickness}"/>
+    <Setter Property="Padding" Value="4"/>
+    <Setter Property="Template">
+      <ControlTemplate>
+        <Border Name="border"
+                Background="{TemplateBinding Background}"
+                BorderBrush="{TemplateBinding BorderBrush}"
+                BorderThickness="{TemplateBinding BorderThickness}">
+          <DockPanel Margin="{TemplateBinding Padding}">
+            
+            <TextBlock Name="floatingWatermark"
+                       Foreground="{DynamicResource ThemeAccentBrush}"
+                       FontSize="{DynamicResource FontSizeSmall}"
+                       Text="{TemplateBinding Watermark}"
+                       DockPanel.Dock="Top">
+              <TextBlock.IsVisible>
+                <MultiBinding Converter="{x:Static BoolConverters.And}">
+                  <Binding RelativeSource="{RelativeSource TemplatedParent}"
+                           Path="UseFloatingWatermark"/>
+                  <Binding RelativeSource="{RelativeSource TemplatedParent}"
+                           Path="DisplayText"
+                           Converter="{x:Static StringConverters.NotNullOrEmpty}"/>
+                </MultiBinding>
+              </TextBlock.IsVisible>
+            </TextBlock>
+
+            <DataValidationErrors>
+              <ScrollViewer HorizontalScrollBarVisibility="{TemplateBinding (ScrollViewer.HorizontalScrollBarVisibility)}"
+                            VerticalScrollBarVisibility="{TemplateBinding (ScrollViewer.VerticalScrollBarVisibility)}">
+                
+                <Panel>
+                  <TextBlock Name="watermark"
+                             Opacity="0.5"
+                             Text="{TemplateBinding Watermark}"
+                             IsVisible="{TemplateBinding Path=Text, Converter={x:Static StringConverters.NullOrEmpty}}"/>
+                  <TextPresenter Name="PART_TextPresenter"
+                                 Text="{TemplateBinding Text, Mode=TwoWay}"
+                                 CaretIndex="{TemplateBinding CaretIndex}"
+                                 SelectionStart="{TemplateBinding SelectionStart}"
+                                 SelectionEnd="{TemplateBinding SelectionEnd}"
+                                 TextAlignment="{TemplateBinding TextAlignment}"
+                                 TextWrapping="{TemplateBinding TextWrapping}"/>
+                </Panel>
+              </ScrollViewer>
+            </DataValidationErrors>
+          </DockPanel>
+        </Border>
+      </ControlTemplate>
+    </Setter>
+  </Style>
+  <Style Selector="TextBox:pointerover /template/ Border#border">
+    <Setter Property="BorderBrush" Value="{DynamicResource ThemeBorderDarkBrush}"/>
+  </Style>
+  <Style Selector="TextBox:focus /template/ Border#border">
+    <Setter Property="BorderBrush" Value="{DynamicResource ThemeBorderDarkBrush}"/>
+  </Style>
+  <Style Selector="TextBox:error /template/ Border#border">
+    <Setter Property="BorderBrush" Value="{DynamicResource ErrorBrush}"/>
+  </Style>
+</Styles>