I’ve just uploaded HTTPDUserAdminContrib that will allow you to use DBM files (a database formated file) and SQL databases (as supported by DBI) for TWiki’s user, password and email address backend.
Combined with apache’s mod_authn_dbm and mod_authn_dbd you thus can integrate TWiki with more tools than ever before.
In fact, this contrib will allow you to authenticate using your Joomla database’s users (please remeber to set registration off, and set the database access to read only ).