code: def from_json(cls, json_data):
      
      return cls(user=json_data['client_email'],
                 keydata=json_data['private_key'],
                 token_uri=json_data['token_uri'])
docs: Create an uploader given (parsed) JSON data.
  
      Note that this is a JSON-formatted key file downloaded from Google when
      the service account key is created, *NOT* a json-encoded
      oauth2client.client.SignedJwtAssertionCredentials object.
  
      Args:
        json_data: Dict containing the loaded JSON key data.
  
      Returns:
        a MfgInspectorCallback with credentials.