right now this is what I have:
// PEAR database DSN for performing the query. By default
// Roundcube DB settings are used.
$rcmail_config['password_db_dsn'] = 'mysql://USERNAME:PASSWORD@localhost/DBNAME';
// Default: "SELECT update_passwd(%c, %u)"
$rcmail_config['password_query'] = 'SELECT update_passwd(%c, %u)';