def add_metadata_columns_to_schema(schema_message):
    """Metadata _sdc columns according to the stitch documentation at
    https://www.stitchdata.com/docs/data-structure/integration-schemas#sdc-columns

    Metadata columns gives information about data injections
    """
    extended_schema_message = schema_message
    extended_schema_message['schema']['properties']['_sdc_extracted_at'] = {'type': ['null', 'string'],
                                                                            'format': 'date-time'}
    extended_schema_message['schema']['properties']['_sdc_batched_at'] = {'type': ['null', 'string'],
                                                                          'format': 'date-time'}
    extended_schema_message['schema']['properties']['_sdc_deleted_at'] = {
        'type': ['null', 'string']}

    return extended_schema_message