protected function getInsertSecurityIdentitySql(SecurityIdentityInterface $sid)
    {
        if ($sid instanceof UserSecurityIdentity) {
            $identifier = $sid->getClass().'-'.$sid->getUsername();
            $username = true;
        } elseif ($sid instanceof RoleSecurityIdentity) {
            $identifier = $sid->getRole();
            $username = false;
        } else {
            throw new \InvalidArgumentException('$sid must either be an instance of UserSecurityIdentity, or RoleSecurityIdentity.');
        }

        return sprintf(
            'INSERT INTO %s (identifier, username) VALUES (%s, %s)',
            $this->options['sid_table_name'],
            $this->connection->quote($identifier),
            $this->connection->getDatabasePlatform()->convertBooleans($username)
        );
    }