[Mediawiki-l] Single-sign one without Extension:CentralAuth?

[Gregor Hagedorn]

We have a wikifarm with a number of wikis and central media
repositories. We are missing a single sign-on - presently, if someone
is signed into a wiki and uploads a file, this one has to sign in a
second time.

The "obvious" solution is to do the same as wikimedia, i.e.
http://www.mediawiki.org/wiki/Extension:CentralAuth

However, the page above warns in no unclear words to rather use
$wgSharedDB (which we already do). But while this offers
single-authorization ("password storage"), it provides no single-sign
on.

Advice? What are our options?

thanks!

Gregor