code: def _load_config(self, client_secrets_file, client_id, client_secret):
          
          if client_id and client_secret:
              self.client_id, self.client_secret = client_id, client_secret
              return
  
          if client_secrets_file:
              self._load_client_secrets(client_secrets_file)
              return
  
          if 'GOOGLE_OAUTH2_CLIENT_SECRETS_FILE' in self.app.config:
              self._load_client_secrets(
                  self.app.config['GOOGLE_OAUTH2_CLIENT_SECRETS_FILE'])
              return
  
          try:
              self.client_id, self.client_secret = (
                  self.app.config['GOOGLE_OAUTH2_CLIENT_ID'],
                  self.app.config['GOOGLE_OAUTH2_CLIENT_SECRET'])
          except KeyError:
              raise ValueError(
                  'OAuth2 configuration could not be found. Either specify the '
                  'client_secrets_file or client_id and client_secret or set '
                  'the app configuration variables '
                  'GOOGLE_OAUTH2_CLIENT_SECRETS_FILE or '
                  'GOOGLE_OAUTH2_CLIENT_ID and GOOGLE_OAUTH2_CLIENT_SECRET.')
docs: Loads oauth2 configuration in order of priority.
  
          Priority:
              1. Config passed to the constructor or init_app.
              2. Config passed via the GOOGLE_OAUTH2_CLIENT_SECRETS_FILE app
                 config.
              3. Config passed via the GOOGLE_OAUTH2_CLIENT_ID and
                 GOOGLE_OAUTH2_CLIENT_SECRET app config.
  
          Raises:
              ValueError if no config could be found.