Enabling Server-Side Access

With the earlier Add Sign-In procedure, your app authenticates the user on the client side only; in that case, you can access the Google APIs only while the user is actively using your app. If you want your servers to be able to make Google API calls on behalf of users—possibly while they are offline—your server requires an access token.

Before you begin

Enable server-side API access for your app

  1. When you configure Google Sign-In, build the GoogleSignInOptions object with the requestServerAuthCode method and specify the scopes that your app's backend needs to access with the requestScopes method.

    Pass your server's client ID to the requestServerAuthCode method.

    // Configure sign-in to request offline access to the user's ID, basic
// profile, and Google Drive. The first time you request a code you will
// be able to exchange it for an access token and refresh token, which
// you should store. In subsequent calls, the code will only result in
// an access token. By asking for profile access (through
// DEFAULT_SIGN_IN) you will also get an ID Token as a result of the
// code exchange.
String serverClientId = getString(R.string.server_client_id);
GoogleSignInOptions gso = new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
        .requestScopes(new Scope(Scopes.DRIVE_APPFOLDER))
        .requestServerAuthCode(serverClientId)
        .requestEmail()
        .build();

  2. After the user successfully signs in, get an auth code for the user with getServerAuthCode:

    Task<GoogleSignInAccount> task = GoogleSignIn.getSignedInAccountFromIntent(data);
try {
    GoogleSignInAccount account = task.getResult(ApiException.class);
    String authCode = account.getServerAuthCode();

    // Show signed-un UI
    updateUI(account);

    // TODO(developer): send code to server and exchange for access/refresh/ID tokens
} catch (ApiException e) {
    Log.w(TAG, "Sign-in failed", e);
    updateUI(null);
}

  3. Send the auth code to your app's backend using HTTPS POST:

    HttpPost httpPost = new HttpPost("https://yourbackend.example.com/authcode");

try {
    List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(1);
    nameValuePairs.add(new BasicNameValuePair("authCode", authCode));
    httpPost.setEntity(new UrlEncodedFormEntity(nameValuePairs));

    HttpResponse response = httpClient.execute(httpPost);
    int statusCode = response.getStatusLine().getStatusCode();
    final String responseBody = EntityUtils.toString(response.getEntity());
} catch (ClientProtocolException e) {
    Log.e(TAG, "Error sending auth code to backend.", e);
} catch (IOException e) {
    Log.e(TAG, "Error sending auth code to backend.", e);
}

  4. On your app's backend server, exchange the auth code for access and refresh tokens. Use the access token to call Google APIs on behalf of the user and, optionally, store the refresh token to acquire a new access token when the access token expires.

    If you requested profile access, you also get an ID token that contains basic profile information for the user.

    For example:

    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']