Lightweight alternative to query.php for authenticating against
CVL Joomla instance.

Includes HTTP response codes.

Used by the isValidCvlUsernameAndPassword method in the CVL
fork of WsgiDAV:

https://github.com/CVL-dev/wsgidav/blob/CVL_SB_UAT_June_2013/wsgidav/http_authenticator.py#L225