Game CenterへログインしたタイミングでLeaderboardからスコアを取得する

NotificationCenter.default.addObserver(
            forName: .GKPlayerAuthenticationDidChangeNotificationName,
            object: nil,
            queue: OperationQueue.main,
            using: { _ in
                // this block is called whether authentication succeeds or fails.
                self.authenticationChanged()
            }
        )

private func authenticationChanged() {
    if GKLocalPlayer.local.isAuthenticated {
        print("You are logged in. Start to load scores from Game Center.")
        // Get the Leaderboard ID of this app that you have previously registered in App Store Connect
        // (only one ID is registered here).
        GKLocalPlayer.local.loadDefaultLeaderboardIdentifier(completionHandler: { (leaderboardIdentifer, error) in
            if error != nil { // Error occured
                print(error!.localizedDescription)
            } else { // Got the loaderBoarderIdentifier for this app.
                // Load scores
                if let leaderboarderId = leaderboardIdentifer {
                    print("Default leaderboardIdentifer is \(leaderboarderId).")
                    GKLeaderboard.loadLeaderboards(IDs: [leaderboarderId]) { (boards, _) in
                        boards?.first?.loadEntries(for: .global, timeScope: .allTime, range: NSRange(location: 1, length: 1), completionHandler: {(local, entries, _, _) in
                            // If entries are loaded, set the value to worldHighScore
                            if let entries = entries,
                               entries.isEmpty == false {
                                self.autoLoadScore.worldScore = entries[0].score
                            }
                            // If local is loaded, set the value to yourHighScore
                            if let local = local {
                                self.autoLoadScore.yourScore = local.score
                            }
                        })
                    }
                }
            }
        })
    }
}