Deletes the Key with check-and-set semantics.

        Parameters:
            key (str): Key to delete
            index (ObjectIndex): Index ID
        Response:
            bool: ``True`` on success

        The Key will only be deleted if its current modify index matches the
        supplied Index.

async def delete_cas(self, key, *, index):
        """Deletes the Key with check-and-set semantics.

        Parameters:
            key (str): Key to delete
            index (ObjectIndex): Index ID
        Response:
            bool: ``True`` on success

        The Key will only be deleted if its current modify index matches the
        supplied Index.
        """
        index = extract_attr(index, keys=["ModifyIndex", "Index"])
        response = await self._discard(key, cas=index)
        return response.body is True