Deletes the Key with check-and-set semantics.

        Parameters:
            key (str): Key to delete
            index (ObjectIndex): Index ID

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

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

        Parameters:
            key (str): Key to delete
            index (ObjectIndex): Index ID

        The Key will only be deleted if its current modify index matches
        the supplied Index
        """
        self.append({
            "Verb": "delete-cas",
            "Key": key,
            "Index": extract_attr(index, keys=["ModifyIndex", "Index"])
        })
        return self