Stretch TextBox in StackPanel - wpf

Question

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?
Thank you in advance!
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="15" />
<RowDefinition Height="15" />
<RowDefinition Height="*" />
<RowDefinition Height="*" />
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="200" />
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<!--ROW 0-->
<TextBlock Text="DOMAIN:"/>
<!--ROW 1-->
<Separator Grid.Row="1" Grid.ColumnSpan="2"/>
<!--ROW 2-->
<TextBlock Text="Connection credentials:" HorizontalAlignment="Left" VerticalAlignment="Center" Grid.Row="2" Grid.Column="0"/>
<StackPanel Orientation="Horizontal" Grid.Row="2" Grid.Column="1">
<Button Content="EDIT" Style="{DynamicResource SquareButtonStyle}" Width="80" Margin="0,0,10,0"/>
<TextBlock x:Name="CurrentCredentialslbl" Text="Connect as:" HorizontalAlignment="Stretch" VerticalAlignment="Center"/>
</StackPanel>
<!--ROW 3-->
<TextBlock Text="Find accounts in domain:" HorizontalAlignment="Left" VerticalAlignment="Center" Grid.Row="3" Grid.Column="0"/>
<StackPanel Orientation="Horizontal" Grid.Row="3" Grid.Column="1">
<TextBox />
<Button Content="Browse" Style="{DynamicResource SquareButtonStyle}" Width="80" Margin="10,0,0,0"/>
</StackPanel>
<!--ROW 4-->
<CheckBox Content="Only search in this container" HorizontalAlignment="Left" VerticalAlignment="Center" Grid.Row="4" Grid.Column="0"/>
</Grid>

Answer 1

Grid with 2 columns instead of StackPanel should fit perfectly
<Grid Grid.Row="3" Grid.Column="1">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*"/>
<ColumnDefinition Width="Auto" />
</Grid.ColumnDefinitions>
<TextBox />
<Button Grid.Column="1"
Content="Browse"
Style="{DynamicResource SquareButtonStyle}"
Width="80" Margin="10,0,0,0"/>
</Grid>