<Storyboard x:Name="StoryboardLogin">
 <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="(Width)" Storyboard.TargetName="LeftColumn">
 <DiscreteObjectKeyFrame KeyTime="0" Value="0"/>
 <DiscreteObjectKeyFrame KeyTime="0:0:0.20" Value="Auto"/>
 </ObjectAnimationUsingKeyFrames>
</Storyboard>

<Grid.ColumnDefinitions>
 <ColumnDefinition x:Name="LeftColumn" />
 <ColumnDefinition />
</Grid.ColumnDefinitions>