So I had a full working solution in iOS7 that displays a LoginViewController via presentViewController in the AppDelegate\'s didFinishLaunching.
Basically I am doing so
You can set the window to an instance of a temporary controller.
self.window.backgroundColor = [UIColor whiteColor]; //do some styling etc.
self.window.rootViewController = [LoginViewController new];
[self.window makeKeyAndVisible];
From the set controller (LoginViewController) you can push your real login controller with the desired transition. Once the login sequence is over you can make a transition from the login controller to the default application root view controller.
[UIView transitionWithView:[AppGlobal sharedApp].applicationWindow
duration:0.75
options:UIViewAnimationOptionTransitionFlipFromLeft
animations:^{
[AppGlobal sharedApp].applicationWindow.rootViewController = [AppRootViewController new];
} completion:nil];