How to generate "client_secret.json" for Google API with offline access?

I am trying to authenticate to Google API in a backend service using a service account. It will not have a UI at all.

I have generated private keys in JSON format from Google Developer Console, using a Service Account but there is no field named "client_secret" in it.

I found this example on GitHub, and its structure should be correctly parsed by GoogleClientSecrets class.

What are the steps to generate the correct client_secret.json as in the GitHub example?

I need to do this again after a long time, and I am documenting the steps as of May 2022.

• Login to Google Cloud Console

• Go to API Service -> Credentials

• Click "+ Create Credentials", ans select Service Account

  • Fill in service account name, it will create a default account id
  • Click "Create and Continue"
  • In the role selection screen, I selected owner as this was my personal project. If your service will be accessed by external parties, consider giving only required permissions
  • Click Continue
  • I did not select any user/admin role on screen 3. Click Done.

• You will be back on Credentials screen. Click the Service account Email you just created.

  • You should be on the Details tab. Click on the KEYS tab.
  • Click "Add Key" dropdown, and click "Create New Key".
  • Select JSON key type (default), and click create.
  • This should download a JSON file to you.

You can then use the credential to access Google services. For example, in my case I access YouTube service with the following code ( clientSecretsStream is the InputStream of that credentials JSON file):

public static YouTube initializeYouTube(InputStream clientSecretsStream, String appName) throws IOException {
    final HttpTransport httpTransport = new NetHttpTransport();
    final JsonFactory jsonFactory = JacksonFactory.getDefaultInstance();

    GoogleCredential credential = GoogleCredential.fromStream(clientSecretsStream)
            .createScoped(Collections.singleton(YouTubeScopes.YOUTUBE_READONLY));

    return new YouTube.Builder(httpTransport, jsonFactory, credential)
            .setApplicationName(appName)
            .build();
}