code: def _set_session():
      
      global __SESSION
      global __USER_ID
      
      if __SESSION is None:
          try:
              __SESSION = AuthorizedSession(google.auth.default(['https://www.googleapis.com/auth/userinfo.profile',
                                                                 'https://www.googleapis.com/auth/userinfo.email'])[0])
              health()
              __USER_ID = id_token.verify_oauth2_token(__SESSION.credentials.id_token,
                                                       Request(session=__SESSION))['email']
          except (DefaultCredentialsError, RefreshError) as gae:
              if os.getenv('SERVER_SOFTWARE', '').startswith('Google App Engine/'):
                  raise
              logging.warning("Unable to determine/refresh application credentials")
              try:
                  subprocess.check_call(['gcloud', 'auth', 'application-default',
                                         'login', '--no-launch-browser'])
                  __SESSION = AuthorizedSession(google.auth.default(['https://www.googleapis.com/auth/userinfo.profile',
                                                                     'https://www.googleapis.com/auth/userinfo.email'])[0])
              except subprocess.CalledProcessError as cpe:
                  if cpe.returncode < 0:
                      logging.exception("%s was terminated by signal %d",
                                        cpe.cmd, -cpe.returncode)
                  else:
                      logging.exception("%s returned %d", cpe.cmd,
                                        cpe.returncode)
                  raise gae
docs: Sets global __SESSION and __USER_ID if they haven't been set