Comment 0 for bug 1872478

Apache is lacking proper support for post-handhake-auth in TLSv1.3 POST requests using certificate authentication.

This was fixed in debian[1] via patches from upstream[2].

Test case:
$ lxc launch ubuntu-daily:focal ubuntu

Enter the container as root:
$ lxc exec ubuntu bash

Verify hostname is "ubuntu":
# hostname
ubuntu

Install apache2:
apt update && apt install apache2

Download the following files from this other bug report and place them in /etc/apache2:
cd /etc/apache2
wget https://bugs.launchpad.net/ubuntu/+source/apache2/+bug/1833039/+attachment/5274492/+files/cacert.pem https://bugs.launchpad.net/ubuntu/+source/apache2/+bug/1833039/+attachment/5274493/+files/ubuntu.pem https://bugs.launchpad.net/ubuntu/+source/apache2/+bug/1833039/+attachment/5274494/+files/ubuntu.key

These certs are luckily still valid until june 2020, so they can be used for this bug as well.

Adjust permissions of the key file:
chmod 0640 /etc/apache2/ubuntu.key
chgrp www-data /etc/apache2/ubuntu.key

Download the client certificate and key files and place them in /root:
cd /root
wget https://bugs.launchpad.net/ubuntu/+source/apache2/+bug/1833039/+attachment/5274495/+files/client-auth.pem https://bugs.launchpad.net/ubuntu/+source/apache2/+bug/1833039/+attachment/5274496/+files/client-auth.key

Create this vhost file (caution, lines may wrap, in particular LogFormat: it should be one long line):
cat > /etc/apache2/sites-available/cert-auth-test.conf <<EOF
<IfModule mod_ssl.c>
    <VirtualHost _default_:443>
        LogLevel info ssl:warn
        ServerAdmin webmaster@localhost
        DocumentRoot /var/www/html
        LogFormat "%h %l %u %t \"%r\" %>s %O \"%{Referer}i\" \"%{User-Agent}i\" protocol=%{SSL_PROTOCOL}x commonName=%{SSL_CLIENT_S_DN_CN}x" combined-ssl
        ErrorLog \${APACHE_LOG_DIR}/error.log
        CustomLog \${APACHE_LOG_DIR}/access.log combined-ssl
        SSLEngine on
        SSLCertificateFile /etc/apache2/ubuntu.pem
        SSLCertificateKeyFile /etc/apache2/ubuntu.key
        SSLCACertificateFile /etc/apache2/cacert.pem
        <FilesMatch "\.(cgi|shtml|phtml|php)$">
                SSLOptions +StdEnvVars
        </FilesMatch>
        <Directory /usr/lib/cgi-bin>
                SSLOptions +StdEnvVars
        </Directory>
        <Location />
                SSLRenegBufferSize 1024
                SSLVerifyClient require
                Require ssl-verify-client
        </Location>
    </VirtualHost>
</IfModule>
EOF

Enable the ssl module and this new vhost we just created:
a2enmod ssl && a2ensite cert-auth-test.conf

Restart apache2:
systemctl restart apache2

Verify that cert authentication is required:
root@ubuntu:~# curl --output index.html https://ubuntu/ --cacert /etc/apache2/cacert.pem --tlsv1.3 -f
  % Total % Received % Xferd Average Speed Time Time Time Current
                                 Dload Upload Total Spent Left Speed
  0 0 0 0 0 0 0 0 --:--:-- --:--:-- --:--:-- 0
curl: (56) OpenSSL SSL_read: error:1409445C:SSL routines:ssl3_read_bytes:tlsv13 alert certificate required, errno 0

Verify that a GET request with the client certificate works:
root@ubuntu:~# curl --output index.html https://ubuntu/ --cacert /etc/apache2/cacert.pem --cert client-auth.pem --key client-auth.key --tlsv1.3 -f
  % Total % Received % Xferd Average Speed Time Time Time Current
                                 Dload Upload Total Spent Left Speed
100 10918 100 10918 0 0 969k 0 --:--:-- --:--:-- --:--:-- 969k

Verify that POST request with the client certificate fails:
root@ubuntu:~# curl --output index.html https://ubuntu/ --cacert /etc/apache2/cacert.pem --cert client-auth.pem --key client-auth.key --tlsv1.3 -f -F bug=true
  % Total % Received % Xferd Average Speed Time Time Time Current
                                 Dload Upload Total Spent Left Speed
100 142 0 0 100 142 0 12909 --:--:-- --:--:-- --:--:-- 14200
curl: (22) The requested URL returned error: 403 Forbidden

Server logs for the above:
==> /var/log/apache2/error.log <==
[Mon Apr 13 14:49:03.357183 2020] [ssl:error] [pid 12248:tid 139782462109440] [client 10.0.100.38:41002] AH02263: Re-negotiation handshake failed: Client certificate missing

==> /var/log/apache2/access.log <==
10.0.100.38 - - [13/Apr/2020:14:49:03 +0000] "POST / HTTP/1.1" 403 3798 "-" "curl/7.68.0" protocol=TLSv1.3 commonName=-

With the fixed packages, the POST request works:
root@ubuntu:~# curl --output index.html https://ubuntu/ --cacert /etc/apache2/cacert.pem --cert client-auth.pem --key client-auth.key --tlsv1.3 -f -F bug=true
  % Total % Received % Xferd Average Speed Time Time Time Current
                                 Dload Upload Total Spent Left Speed
100 11060 100 10918 100 142 101k 1352 --:--:-- --:--:-- --:--:-- 102k

And the server log confirms it was a POST request, using certificates, and TLSv1.3:
==> /var/log/apache2/access.log <==
10.0.100.38 - - [13/Apr/2020:14:52:26 +0000] "POST / HTTP/1.1" 200 17118 "-" "curl/7.68.0" protocol=TLSv1.3 commonName=client-auth