class Google::Auth::ExternalAccount::PluggableAuthCredentials

def load_subject_token_from_output_file
  return nil if @credential_source_executable_output_file.nil?
  return nil unless File.exist? @credential_source_executable_output_file
  begin
    content = File.read @credential_source_executable_output_file, encoding: "utf-8"
    response = MultiJson.load content, symbolize_keys: true
  rescue StandardError
    return nil
  end
  begin
    subject_token = parse_subject_token response
  rescue StandardError => e
    return nil if e.message.match(/The token returned by the executable is expired/)
    raise e
  end
  subject_token
end