Comment 40 for bug 1833039

Cosmic verification
Confirming the bug with the distro packages:
 *** 2.4.34-1ubuntu2.1 500
        500 http://br.archive.ubuntu.com/ubuntu cosmic-updates/main amd64 Packages

index is downloaded, but after a long delay:
# curl --output index.html https://ubuntu/ --cacert /etc/apache2/cacert.pem --cert client-auth.pem --key client-auth.key --tlsv1.2
  % Total % Received % Xferd Average Speed Time Time Time Current
                                 Dload Upload Total Spent Left Speed
100 10918 100 10918 0 0 705 0 0:00:15 0:00:15 --:--:-- 2567

access log confirms the client certificate was used:
10.0.100.50 - - [05/Jul/2019:13:40:32 +0000] "GET / HTTP/1.1" 200 16544 "-" "curl/7.61.0" protocol=TLSv1.2 commonName=client-auth

Updating apache and repeating the download:
 *** 2.4.34-1ubuntu2.2 500
        500 http://br.archive.ubuntu.com/ubuntu cosmic-proposed/main amd64 Packages

Now it's fast:
# curl --output index.html https://ubuntu/ --cacert /etc/apache2/cacert.pem --cert client-auth.pem --key client-auth.key --tlsv1.2
  % Total % Received % Xferd Average Speed Time Time Time Current
                                 Dload Upload Total Spent Left Speed
100 10918 100 10918 0 0 1332k 0 --:--:-- --:--:-- --:--:-- 1332k

Log confirms client certificate authentication is still being used:
10.0.100.50 - - [05/Jul/2019:13:58:13 +0000] "GET / HTTP/1.1" 200 16525 "-" "curl/7.61.0" protocol=TLSv1.2 commonName=client-auth

The slight difference in downloaded data (16544 vs 16525) is due to less tls keep-alive pings in the success case. The md5 of index.html is identical:
# md5sum index.html*
3526531ccd6c6a1d2340574a305a18f8 index.html
3526531ccd6c6a1d2340574a305a18f8 index.html-before

Cosmic verification succeeded.