I tried to use this plugin with another database in the same server (localhost) and had the same problem as mikkelbreum. This happens because you are setting another connection with the same server and then closing it.

To solve this problem you have to modify in plugins/authentication/extdb.php, instead of mysql_connect you have to change it for mysql_pconnect. That worked for me.

Also I set in the response another parameters such as the gid and usertype to avoid permission problems.

It would be nice if the gacl permissions could be set from the external database as well. I don't know if this is possible yet but I'm working on that I'll let you know if I get something.

I know it does say 'external' db. But it would be nice if it could also use an alternate DB on same server. However, if you set 'Database Host' to 'localhost' you will not be able to log in as admin anymore!! be aware! If you set this plugin to use localhost, then logging in to admin area will result in denied acces and this error:
Warning: mysql_real_escape_string(): 26 is not
a valid MySQL-Link resource in /home/www/user/html/sitename/libraries/joomla/database/database/mysql.php on line 193 or something like that..

in case this happens go to your db admin (phpmyadmin maybe?) and there set the published status of the plugin to 0.

I installed this plug-in and it worked right away! Simply great.

I do have one suggestion however: it would be great if this plugin would support sub-query's, or would enable the administrator to manually specify the query to use.

The current structure of the plug-in requires me to save the user username/password in the same table as the other user data (like first name, surname). I would like to be able to keep these kinds of data seperated.

It just works!
Set up the database info and off you go.
Exactly what I needed.

The latest release (0.9) now supports both plain text and SHA-1 type passwords.

This plugin may be still in development so I only want to comment on a limitation I experienced, not to be critical.

The configuration of the module has a dropdown box to choose what kind of password is to be used. The only option is to use a MD5 hash of the password. I would have expected a plain text option as many apps use a plain text password for easier integration with other systems.

I hope the developer continues to develop a v 1.5 version of database authentication from an external MySQL db.

this was the plugin to use with moodle and really works !!!