setting root view controller in app delegate

AppDelegate.swift

class AppDelegate: UIResponder, UIApplicationDelegate, SpotifyAuthDelegate {
    
    var window: UIWindow?
    
    var navigationController: UINavigationController = UINavigationController()

    private var auth: SpotifyAuth {
        return SpotifyAuth.shared
    }
    
    private var rootViewController: UIViewController {
        return SpotifyAuth.shared.isAuthenticated ? YesViewController() : ViewController()
    }
    
    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
        
        auth.delegate = self
        
        self.window = UIWindow(frame: UIScreen.main.bounds)
        
        let storyboard: UIStoryboard = UIStoryboard(name: "Main", bundle: nil)
        navigationController = storyboard.instantiateInitialViewController() as! UINavigationController
        navigationController.viewControllers = [rootViewController]
        self.window?.rootViewController = navigationController
        self.window?.makeKeyAndVisible()

        return true
    }
    
    func application(_ app: UIApplication, open url: URL, options: [UIApplicationOpenURLOptionsKey : Any] = [:]) -> Bool {
        auth.handle(authenticationURL: url)
        auth.fetchAccessToken()
        return true
    }
    
    // MARK: - SpotifyAuthDelegate
    
    func sessionUpdated(in spotifyAuth: SpotifyAuth) {
        navigationController.setViewControllers([rootViewController], animated: false)
    }
}