如何使用objective-c获取Gmail api的访问令牌

#import <GoogleSignIn/GoogleSignIn.h>

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    // 其他代码...
    
    // 初始化Google Sign-In
    [GIDSignIn sharedInstance].clientID = @"YOUR_CLIENT_ID";
    
    return YES;
}

#import <GoogleSignIn/GoogleSignIn.h>

// ...

- (void)signInWithGoogle {
    GIDSignIn *signIn = [GIDSignIn sharedInstance];
    signIn.delegate = self;
    signIn.presentingViewController = self;
    signIn.scopes = @[@"https://www.googleapis.com/auth/gmail.readonly"];
    [signIn signIn];
}

// GIDSignInDelegate方法
- (void)signIn:(GIDSignIn *)signIn didSignInForUser:(GIDGoogleUser *)user withError:(NSError *)error {
    if (error == nil) {
        NSString *accessToken = user.authentication.accessToken;
        // 使用accessToken进行Gmail API的访问
    } else {
        NSLog(@"Google Sign-In Error: %@", error.localizedDescription);
    }
}