Video Link:

Google Developer Console : https://play.google.com/apps/publish/

Helper Files Link : https://github.com/cpinan/Cocos2dX_GooglePlayGamesServices – credit to Carlos Eduardo Piñan Indacochea

AppController.h

#import <UIKit/UIKit.h>

#import <GooglePlus/GooglePlus.h>
#import <GooglePlayGames/GooglePlayGames.h>

@class RootViewController;

@interface AppController : NSObject <UIApplicationDelegate, GPPSignInDelegate> {
    UIWindow *window;
    RootViewController *viewController;
}

@property (nonatomic, retain) UIWindow *window;
@property(nonatomic, readonly) RootViewController* viewController;

@end

Functions to add to AppController.mm

#pragma mark - Google Play Game Services

- (void)playServicesAuthenticate
{
    NSLog(@"Authenticate");
    PlayGameSingleton::sharedInstance().authenticate();
}

- (BOOL)application:(UIApplication *)application
            openURL:(NSURL *)url
  sourceApplication:(NSString *)sourceApplication
         annotation:(id)annotation {
    return [GPPURLHandler handleURL:url sourceApplication:sourceApplication annotation:annotation];
}

- (void)finishedWithAuth:(GTMOAuth2Authentication *)auth error:(NSError *)error
{
    NSLog(@"Finished with auth.");
    //if (error == nil && auth) {
    //NSLog(@"Success signing in to Google! Auth object is %@", auth);
    
    if (error.code == 0 && auth) {
        NSLog(@"Success signing in to Google! Auth object is %@", auth);
        
        // Tell your GPGManager that you're ready to go.
        [self startGoogleGamesSignIn];
        
    } else {
        NSLog(@"Failed to log into Google\n\tError=%@\n\tAuthObj=%@",error,auth);
    }
}

-(void)startGoogleGamesSignIn
{
    // The GPPSignIn object has an auth token now. Pass it to the GPGManager.
    [[GPGManager sharedInstance] signIn:[GPPSignIn sharedInstance]
                     reauthorizeHandler:^(BOOL requiresKeychainWipe, NSError *error) {
                         // If you hit this, auth has failed and you need to authenticate.
                         // Most likely you can refresh behind the scenes
                         if (requiresKeychainWipe) {
                             [[GPPSignIn sharedInstance] signOut];
                         }
                         //[[GPPSignIn sharedInstance] authenticate];
                     }];
}

Code to add to the didFinishLaunchingWithOptions function in AppController.mm

// GOOGLE PLAY SERVICES
    
    GPPSignIn* signIn = [GPPSignIn sharedInstance];
    signIn.clientID = [NSString stringWithUTF8String:kClientID];
    signIn.scopes = [NSArray arrayWithObjects:
                     @"https://www.googleapis.com/auth/games",
                     @"https://www.googleapis.com/auth/appstate",
                     nil];
    signIn.language = [[NSLocale preferredLanguages] objectAtIndex:0];
    signIn.delegate = self;
    signIn.shouldFetchGoogleUserID = YES;
    
    
    [GPGManager sharedInstance].achievementUnlockedToastPlacement = kGPGToastPlacementBottom;
    
    if(!PlayGameSingleton::sharedInstance().isSignedIn())
    {
        //[NSThread detachNewThreadSelector:@selector(playServicesAuthenticate) toTarget:self withObject:nil];
    }
    
    // GOOGLE PLAY SERVICES END

Frameworks to add to project:

• AddressBook.framework
• AssetsLibrary.framework
• CoreData.framework
• CoreLocation.framework
• CoreMotion.framework
• CoreTelephony.framework
• CoreText.framework
• Foundation.framework
• MediaPlayer.framework
• QuartzCore.framework
• Security.framework
• SystemConfiguration.framework
• libc++.dylib
• libz.dylib
• GameController.framework (Only if supporting iOS 7+ otherwise follow the fix in the video)

Gaz