Revoke credential that input revocation registry identifier and
        credential revocation identifier specify.

        Return (epoch seconds) time of revocation.

        Raise AbsentTails if no tails file is available for input
        revocation registry identifier. Raise BadRevocation if issuer cannot
        revoke specified credential for any other reason (e.g., did not issue it,
        already revoked it).

        :param rr_id: revocation registry identifier
        :param cr_id: credential revocation identifier
        :return: time of revocation, in epoch seconds

async def revoke_cred(self, rr_id: str, cr_id) -> int:
        """
        Revoke credential that input revocation registry identifier and
        credential revocation identifier specify.

        Return (epoch seconds) time of revocation.

        Raise AbsentTails if no tails file is available for input
        revocation registry identifier. Raise BadRevocation if issuer cannot
        revoke specified credential for any other reason (e.g., did not issue it,
        already revoked it).

        :param rr_id: revocation registry identifier
        :param cr_id: credential revocation identifier
        :return: time of revocation, in epoch seconds
        """

        LOGGER.debug('Issuer.revoke_cred >>> rr_id: %s, cr_id: %s', rr_id, cr_id)

        tails_reader_handle = (await Tails(
            self._dir_tails,
            *rev_reg_id2cred_def_id__tag(rr_id)).open()).reader_handle
        try:
            rrd_json = await anoncreds.issuer_revoke_credential(
                self.wallet.handle,
                tails_reader_handle,
                rr_id,
                cr_id)
        except IndyError as x_indy:
            LOGGER.debug(
                'Issuer.revoke_cred: <!< Could not revoke revoc reg id %s, cred rev id %s: indy error code %s',
                rr_id,
                cr_id,
                x_indy.error_code)
            raise BadRevocation(
                'Could not revoke revoc reg id {}, cred rev id {}: indy error code {}'.format(
                    rr_id,
                    cr_id,
                    x_indy.error_code))

        rre_req_json = await ledger.build_revoc_reg_entry_request(self.did, rr_id, 'CL_ACCUM', rrd_json)
        resp_json = await self._sign_submit(rre_req_json)
        resp = json.loads(resp_json)

        rv = resp['result']['txnMetadata']['txnTime']
        LOGGER.debug('Issuer.revoke_cred <<< %s', rv)
        return rv