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.

def from_json(cls, json_data):
    """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.
    """
    return cls(user=json_data['client_email'],
               keydata=json_data['private_key'],
               token_uri=json_data['token_uri'])