I was looking for something that would allow users to use an external database as their login source for their Joomla site. The External DB Authentication plugin was the answer, but it was outdated already.
Therefore, new life has been breathed into an old plugin. This plugin allows the use of an external MySQL database for authentication into Joomla. It is required that you know the encryption method for the passwords stored in the external database and allows you to use MD5, SHA1, CRYPT (Linux only), plaintext or enter the hash/salt method yourself. It doesn't allow updating from the Joomla end back into the external authentication source.