RHOAuthUtils methods to signIn and signOut of Endpoints OAuth

iOSEndpointsSignIn.m

#pragma mark - Sign in / sign out utils

// Revoke the authorizer and clear the saved authorizer.
+ (void) signOut {
    [GTMOAuth2ViewControllerTouch removeAuthFromKeychainForName:kKeychainItemName];
    [GTMOAuth2ViewControllerTouch revokeTokenForGoogleAuthentication:__authorizer];
    [RHOAuthUtils _setAuthorizer:nil];
}


+ (void) signInFromViewController:(UIViewController*) parentViewController
                     withCallback:(void (^)(NSError* error)) callback {
    __parentViewControllerForSignInModal = parentViewController;
    __signInCallback = callback;
    GTMOAuth2ViewControllerTouch* signInViewController;
    signInViewController = [[GTMOAuth2ViewControllerTouch alloc] initWithScope:kScope
                                                                      clientID:kIosClientID
                                                                  clientSecret:kIosClientSecret
                                                              keychainItemName:kKeychainItemName
                                                                      delegate:self
                                                              finishedSelector:@selector(_viewController:finishedWithAuth:error:)];

    // Display the signInViewController within a Navigation Controller so we can add a cancel button in the top bar.
    UINavigationController *navigationController = [[UINavigationController alloc] initWithRootViewController:signInViewController];
    navigationController.navigationBar.topItem.leftBarButtonItem = [[UIBarButtonItem alloc]
                                                                    initWithTitle:@"Cancel"
                                                                    style:UIBarButtonItemStyleBordered
                                                                    target:self
                                                                    action:@selector(_cancelSignIn)];
    navigationController.navigationBar.barStyle = UIBarStyleBlack;
    navigationController.navigationBar.translucent = NO;
    [parentViewController presentViewController:navigationController animated:YES completion:nil];
}


# pragma mark - private methods

// Called when a user presses Cancel from the Sign in modal.
+ (void) _cancelSignIn {
    [__parentViewControllerForSignInModal dismissViewControllerAnimated:YES completion:nil];
}

// Called when a user completes Sign in.
+ (void) _viewController:(GTMOAuth2ViewControllerTouch*) viewController
        finishedWithAuth:(GTMOAuth2Authentication*) auth
                   error:(NSError*) error {
    if (error != nil) {
        // Authentication failed.
        [RHOAuthUtils signOut];
    } else {
        // Authentication succeeded.
        NSLog(@"Authentication success!");
        [RHOAuthUtils _setAuthorizer:auth];  // Important!!!
    }
    if (![__parentViewControllerForSignInModal.presentedViewController isBeingDismissed]) {
        [__parentViewControllerForSignInModal dismissViewControllerAnimated:NO completion:nil];
    }
    __signInCallback(error);
    __parentViewControllerForSignInModal = nil;
    __signInCallback = nil;
}