从您的应用后端访问 Google API

如果您希望服务器能够代表用户或在用户离线时调用 Google API，请按照此过程操作。

准备工作

您必须完成基本的 Google 登录功能集成。

为您的应用启用服务器端 API 访问权限

在 iOS 应用中的“访问 Google API” 页面上，您的应用仅在客户端对用户进行身份验证；在这种情况下， 只有当用户正在积极使用 您的应用时，您的应用才能访问 Google API。

按照本页介绍的过程，您的服务器可以在用户离线时代表用户调用 Google API。例如，照片应用可以通过在后端服务器上处理照片并将其上传到另一个相册，来增强用户 Google 相册中的照片。为此，您的服务器需要访问令牌和刷新令牌。

如需获取服务器的访问令牌和刷新令牌，您可以 请求一次性授权代码，服务器会使用该代码来换取 这两个令牌。登录成功后，您会发现一次性代码是 serverAuthCode 的 GIDSignInResult 属性。

1. 如果您尚未获取服务器客户端 ID，请获取一个 并在应用的 Info.plist 文件中指定该 ID，位于 OAuth 客户端 ID 下方。

   <key>GIDServerClientID</key>
   <string>YOUR_SERVER_CLIENT_ID</string>

2. 在登录回调中，检索一次性授权代码：

   Swift

   GIDSignIn.sharedInstance.signIn(withPresenting: self) { signInResult, error in
       guard error == nil else { return }
       guard let signInResult = signInResult else { return }
   
       let authCode = signInResult.serverAuthCode
   }
   

   Objective-C

   [GIDSignIn.sharedInstance
             signInWithPresentingViewController:self
                                     completion:^(GIDSignInResult * _Nullable signInResult,
                                                  NSError * _Nullable error) {
         if (error) { return; }
         if (signInResult == nil) { return; }
   
         NSString *authCode = signInResult.serverAuthCode;
   }];
   

3. 使用 HTTPS POST 安全地将 serverAuthCode 字符串传递给您的服务器。

4. 在应用的后端服务器上，使用授权代码换取访问令牌和刷新令牌。使用访问令牌代表用户调用 Google API，还可以选择存储刷新令牌，以便在访问令牌到期时获取新的访问令牌。

   例如：

   Java

   // (Receive authCode via HTTPS POST)
   
   
   if (request.getHeader("X-Requested-With") == null) {
     // Without the `X-Requested-With` header, this request could be forged. Aborts.
   }
   
   // Set path to the Web application client_secret_*.json file you downloaded from the
   // Google API Console: https://console.cloud.google.com/apis/credentials
   // You can also find your Web application client ID and client secret from the
   // console and specify them directly when you create the GoogleAuthorizationCodeTokenRequest
   // object.
   String CLIENT_SECRET_FILE = "/path/to/client_secret.json";
   
   // Exchange auth code for access token
   GoogleClientSecrets clientSecrets =
       GoogleClientSecrets.load(
           JacksonFactory.getDefaultInstance(), new FileReader(CLIENT_SECRET_FILE));
   GoogleTokenResponse tokenResponse =
             new GoogleAuthorizationCodeTokenRequest(
                 new NetHttpTransport(),
                 JacksonFactory.getDefaultInstance(),
                 "https://oauth2.googleapis.com/token",
                 clientSecrets.getDetails().getClientId(),
                 clientSecrets.getDetails().getClientSecret(),
                 authCode,
                 REDIRECT_URI)  // Specify the same redirect URI that you use with your web
                                // app. If you don't have a web version of your app, you can
                                // specify an empty string.
                 .execute();
   
   String accessToken = tokenResponse.getAccessToken();
   
   // Use access token to call API
   GoogleCredential credential = new GoogleCredential().setAccessToken(accessToken);
   Drive drive =
       new Drive.Builder(new NetHttpTransport(), JacksonFactory.getDefaultInstance(), credential)
           .setApplicationName("Auth Code Exchange Demo")
           .build();
   File file = drive.files().get("appfolder").execute();
   
   // Get profile info from ID token
   GoogleIdToken idToken = tokenResponse.parseIdToken();
   GoogleIdToken.Payload payload = idToken.getPayload();
   String userId = payload.getSubject();  // Use this value as a key to identify a user.
   String email = payload.getEmail();
   boolean emailVerified = Boolean.valueOf(payload.getEmailVerified());
   String name = (String) payload.get("name");
   String pictureUrl = (String) payload.get("picture");
   String locale = (String) payload.get("locale");
   String familyName = (String) payload.get("family_name");
   String givenName = (String) payload.get("given_name");

   Python

   from apiclient import discovery
   import httplib2
   from oauth2client import client
   
   # (Receive auth_code by HTTPS POST)
   
   
   # If this request does not have `X-Requested-With` header, this could be a CSRF
   if not request.headers.get('X-Requested-With'):
       abort(403)
   
   # Set path to the Web application client_secret_*.json file you downloaded from the
   # Google API Console: https://console.cloud.google.com/apis/credentials
   CLIENT_SECRET_FILE = '/path/to/client_secret.json'
   
   # Exchange auth code for access token, refresh token, and ID token
   credentials = client.credentials_from_clientsecrets_and_code(
       CLIENT_SECRET_FILE,
       ['https://www.googleapis.com/auth/drive.appdata', 'profile', 'email'],
       auth_code)
   
   # Call Google API
   http_auth = credentials.authorize(httplib2.Http())
   drive_service = discovery.build('drive', 'v3', http=http_auth)
   appfolder = drive_service.files().get(fileId='appfolder').execute()
   
   # Get profile info from ID token
   userid = credentials.id_token['sub']
   email = credentials.id_token['email']