protected function _authInitialResponse($method, $ir, $username = null)
    {
        $cmd = $this->_command('AUTHENTICATE')->add($method);

        if ($this->_capability('SASL-IR')) {
            // IMAP Extension for SASL Initial Client Response (RFC 4959)
            $cmd->add($ir);
            if ($username) {
                $cmd->debug = array(
                    sprintf('AUTHENTICATE %s [INITIAL CLIENT RESPONSE (username: %s)]', $method, $username)
                );
            }
        } else {
            $cmd->add(
                new Horde_Imap_Client_Interaction_Command_Continuation(function($ob) use ($ir) {
                    return new Horde_Imap_Client_Data_Format_List($ir);
                })
            );
            if ($username) {
                $cmd->debug = array(
                    null,
                    sprintf('[INITIAL CLIENT RESPONSE (username: %s)]', $username)
                );
            }
        }

        return $cmd;
    }