SSO/HTTP
From Authentication Tools for Joomla! (JAuthTools)
HTTP Authentication utilises server provided authentication mechanisms to identify and authorize the users request.
For Apache, numerous solutions do exist, a small selection below:
For IIS, there are limited options:
For either major system, further user details rely on parent schemes (e.g. LDAP provided by AD/eDirectory; MySQL DB with user information) provided by Users Sources to autocreate and manage users if necessary.
Note: Joomla! 1.0.x users are able to use this specific method through the HTTP SSO mambot.