This page lists contributed 'external authentication scripts' which can be used to authenticate users against systems that might be not yet supported out-of-the-box by ejabberd. For more information see "How can I authenticate my users against ... ?".
Please remember that if you use an external authentication script, your Jabber client must be configured to allow plaintext login, otherwise you can't login.
The external authentication system is described in the ejabberd Developers Guide, which is included with ejabberd in doc/dev.html.