How to make UILabel resize to fit text
<p>I have a UILabel that I have layed out in a storyboard centred in the view. It has some initial text "tap to login".</p>

<p>I am changing the value of the label to be the user's name once they have logged in. Once I do this, the label is no longer centered as the UILabel has not changed size.</p>

<p>How can I do this with autolayout in interface builder?</p>