Swift: Prevent flicker when presenting login screen at startup
<p>We have two storyboards in our app.  The default view in storyboard #1 assumes the user has previously supplied valid credentials.  If they have not done so we "redirect" to the login screen in storyboard #2:</p>

<pre><code>let storyboard = UIStoryboard(name: "Authentication", bundle: nil)
let controller = storyboard.instantiateViewControllerWithIdentifier("LoginController") as UIViewController
presentViewController(controller, animated: true, completion: nil)
</code></pre>

<p>This works - but there is a flicker when this code runs where the default view briefly appears prior to the login view being displayed.  How can you perform this action without a flicker?</p>