Dude, what are you talking about? The user's credentials are encoded into the HTTP request header "Authorization". In my question I showed how one can unencode it and compare against part of the path at the same HTTP request.
I already figured out how to solve my problem, BTW. I did it with directive LocationMatch with regexp detecting slashes at the end of the location (and Indexes option enabled) and using authorization containter via RequireAll, with two conditions (one is using env. variable setted up earlier). But what are YOU talking about?.. Who the hell is using .htaccess anyways? It is obsolete as hell. And the question was how to enable autoindex for a certain user if it is browsing their home directory. Please read the topic before answering next time.