def derive_operable_regions(ssm_params, regions):
    """
    Given a list of allowed regions from param store, and a list of
    enabled regions in the account, then return a list of regions
    that is in ssm_params AND in regions

    Args:
        ssm_params: dict with region values as keys
        regions: list of regions

    Returns: master list of regions
    """
    return list(set(regions).intersection(list(ssm_params.keys())))