Past Proposals for HTTP Auth Logout

Hello,

I appologize in advance if this is not an appropriate place to ask
this question.

I'm doing some research and I'm interested in learning about any past
proposals to augment HTTP authentication (basic/digest) with a logout
feature.  I have spent several hours reading mailing list archives and
searching the web, and while I've found plenty of related information,
I'm surprised to find no concrete proposals for this feature.

Surely I'm missing something.  Could someone point me in the right
direction?

Thanks much,
tim