code: func ComputeTokenSource(account string) oauth2.TokenSource {
  	return oauth2.ReuseTokenSource(nil, computeSource{account: account})
  }
docs: // ComputeTokenSource returns a token source that fetches access tokens
  // from Google Compute Engine (GCE)'s metadata server. It's only valid to use
  // this token source if your program is running on a GCE instance.
  // If no account is specified, "default" is used.
  // Further information about retrieving access tokens from the GCE metadata
  // server can be found at https://cloud.google.com/compute/docs/authentication.