透過應用程式後端存取 Google API

如果您希望伺服器能夠代表使用者或離線時發出 Google API 呼叫，請按照下列程序操作。

事前準備

您必須完成基本 Google 登入整合。

為應用程式啟用伺服器端 API 存取權

在「在 iOS 應用程式中存取 Google API」頁面上，應用程式只會在用戶端驗證使用者；在這種情況下，應用程式只有在使用者主動使用應用程式時才能存取 Google API。

按照本頁所述的程序進行，您的伺服器可在使用者離線時，代表使用者發出 Google API 呼叫。舉例來說，相片應用程式可透過後端伺服器處理相片，並將結果上傳至另一個相簿，藉此強化使用者的 Google 相簿相簿中的相片。如果要這麼做，您的伺服器會需要存取權杖和更新權杖。

如要為伺服器取得存取權杖和更新權杖，您可以要求伺服器交換這兩個權杖的一次性授權碼。成功登入後，您會看到一次性程式碼，做為 GIDSignInResult 的 serverAuthCode 屬性。

  1. 如果您尚未取得伺服器用戶端 ID，請先在應用程式的 Info.plist 檔案中 (OAuth 用戶端 ID 下方) 指定這個 ID。

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

  2. 在登入回呼中，擷取一次性授權碼：

    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 安全地將 serverAuthCode 字串傳遞至伺服器。

  4. 在應用程式的後端伺服器上，以驗證碼交換存取權及更新權杖。使用存取權杖以代表使用者呼叫 Google API，並視需要儲存更新權杖以在存取權杖過期時取得新的存取權杖。

    範例如下：

    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']