Return the role ARN whose credentials are used to call the API.
    Throws an exception if
    Args:
        sagemaker_session(Session): Current sagemaker session
    Returns:
        (str): The role ARN

def get_execution_role(sagemaker_session=None):
    """Return the role ARN whose credentials are used to call the API.
    Throws an exception if
    Args:
        sagemaker_session(Session): Current sagemaker session
    Returns:
        (str): The role ARN
    """
    if not sagemaker_session:
        sagemaker_session = Session()
    arn = sagemaker_session.get_caller_identity_arn()

    if ':role/' in arn:
        return arn
    message = 'The current AWS identity is not a role: {}, therefore it cannot be used as a SageMaker execution role'
    raise ValueError(message.format(arn))