def get_bucket_acl(self, bucket):
        """
        Get the access control policy for a bucket.
        """
        details = self._details(
            method=b"GET",
            url_context=self._url_context(bucket=bucket, object_name="?acl"),
        )
        d = self._submit(self._query_factory(details))
        d.addCallback(self._parse_acl)
        return d