code: func DefaultTokenSource(ctx context.Context, scope ...string) (oauth2.TokenSource, error) {
  	creds, err := FindDefaultCredentials(ctx, scope...)
  	if err != nil {
  		return nil, err
  	}
  	return creds.TokenSource, nil
  }
docs: // DefaultTokenSource returns the token source for
  // "Application Default Credentials".
  // It is a shortcut for FindDefaultCredentials(ctx, scope).TokenSource.