Login is a sample app that shows how to insert a login view in to UINavigationController backed application. The sample shows how to provide a LogOut exit action, to be used from other views and how to handle a successful login.
The app is based on the Master/Detail template project with all the code isolated to a single LoginController, plus minor Storyboard configuration.
I didn't think this was complex enough a problem to require a blog post, but if anyone disagrees, let me know and I'll write one up on my blog.