Stretch TextBox in StackPanel
<p>This is the current XAML i'm using to do this... and for the life of me cannot figure out how to expand the textbox to fill the entire column. Could anyone please guide me in the correct direction?</p>

<p>Thank you in advance!</p>

<p><a href="https://i.stack.imgur.com/foDDz.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/foDDz.png" alt="Picture of issue"></a></p>

<pre><code>&lt;Grid&gt;        
    &lt;Grid.RowDefinitions&gt;
        &lt;RowDefinition Height="15" /&gt;
        &lt;RowDefinition Height="15" /&gt;
        &lt;RowDefinition Height="*" /&gt;
        &lt;RowDefinition Height="*" /&gt;
        &lt;RowDefinition Height="*" /&gt;
    &lt;/Grid.RowDefinitions&gt;

    &lt;Grid.ColumnDefinitions&gt;
        &lt;ColumnDefinition Width="200" /&gt;
        &lt;ColumnDefinition Width="*"/&gt;
    &lt;/Grid.ColumnDefinitions&gt;

    &lt;!--ROW 0--&gt;
    &lt;TextBlock Text="DOMAIN:"/&gt;
    &lt;!--ROW 1--&gt;
    &lt;Separator Grid.Row="1" Grid.ColumnSpan="2"/&gt;

    &lt;!--ROW 2--&gt;
    &lt;TextBlock  Text="Connection credentials:" HorizontalAlignment="Left" VerticalAlignment="Center" Grid.Row="2" Grid.Column="0"/&gt;
    &lt;StackPanel Orientation="Horizontal" Grid.Row="2" Grid.Column="1"&gt;
        &lt;Button Content="EDIT" Style="{DynamicResource SquareButtonStyle}" Width="80" Margin="0,0,10,0"/&gt;
        &lt;TextBlock x:Name="CurrentCredentialslbl" Text="Connect as:" HorizontalAlignment="Stretch" VerticalAlignment="Center"/&gt;
    &lt;/StackPanel&gt;

    &lt;!--ROW 3--&gt;
    &lt;TextBlock  Text="Find accounts in domain:" HorizontalAlignment="Left" VerticalAlignment="Center" Grid.Row="3" Grid.Column="0"/&gt;
    &lt;StackPanel Orientation="Horizontal" Grid.Row="3" Grid.Column="1"&gt;
        &lt;TextBox /&gt;
        &lt;Button Content="Browse" Style="{DynamicResource SquareButtonStyle}" Width="80" Margin="10,0,0,0"/&gt;
    &lt;/StackPanel&gt;

    &lt;!--ROW 4--&gt;
    &lt;CheckBox  Content="Only search in this container" HorizontalAlignment="Left" VerticalAlignment="Center" Grid.Row="4" Grid.Column="0"/&gt;
&lt;/Grid&gt;
</code></pre>