On Ubuntu 15.10, after activating Apache with TLS, doing the workaround described on bug 5576, tlclient.cgi still does not work: The content is displayed, instead of the CGI executing. This can be fixed with:
# sudo a2enmod cgi
# service apache2 restart
Perhaps tl-setup should do that?
Same problem on Ubuntu 14.04.
Solved by mentioning the requirement in the new documentation written for bug 5190.
Verified that I could get a working setup following Web Integration documentation.