code: def _authenticate(secrets_file):
      
      flow = oauthclient.flow_from_clientsecrets(
          secrets_file,
          scope=OAUTH_SCOPE,
          message=('Failed to initialized OAuth 2.0 flow with secrets '
                   'file: %s' % secrets_file))
      storage = oauthfile.Storage(OAUTH_CREDENTIALS_FILE)
      credentials = storage.get()
      if credentials is None or credentials.invalid:
          credentials = oauthtools.run_flow(flow, storage, oauthtools.argparser.parse_args(args=[]))
      http = httplib2.Http()
      return credentials.authorize(http)
docs: Runs the OAuth 2.0 installed application flow.
  
      Returns:
        An authorized httplib2.Http instance.