Login to web server with Google Sign-in - download

Question

I'm connecting to a 3rd party web server from an HTTP client (Java or Dart - Android app) to download some resources (XML or IMG files) that belong to the current user on that server. This site requires login with Google Sing-In. I have everything set up in my Android app to login the user with Google, I obtained their authorization idToken. But how do actually use it in HTTP GET or POST methods to download the protected resources?
With BASIC authentication it's easy - just set HTTP 'Authorization' header correctly ("Basic " + user:password encoded as base64), call GET, and I download the desired resource. But I cannot find any information on how to do this with Google Sing-In. Do I send the idToken I received from Google in some headers? What other magic is needed?

Answer 1

Adding a Java code snippet, hope it helps:
// (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.developers.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://www.googleapis.com/oauth2/v4/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");
For detailed info, find all the required steps and references at: https://developers.google.com/identity/sign-in/web/server-side-flow#step_1_create_a_client_id_and_client_secret