Comment 1 for bug 1835929

$ lxc exec bionic-19-032-1 -- bash
$ uname -a
Linux bionic-19-032-1 4.15.0-54-generic #58-Ubuntu SMP Mon Jun 24 10:55:24 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
$ cat /etc/lsb-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=18.04
DISTRIB_CODENAME=bionic
DISTRIB_DESCRIPTION="Ubuntu 18.04.2 LTS"

$ apt-get -y install backuppc
$ apt-get -y install lynx

### Reset password to 'password' or whatever
$ htpasswd /etc/backuppc/htpasswd backuppc

$ lynx bionic-19-032-1
This prompts for basic auth, entered:
  username: backuppc
  password: password

This then shows binary garbage, starting with "ELF>@@8 @@@@88 8@..."

Opening the lxc container's network in firefox also prompts for auth, and then displays a dialog:

-----------------------------
"You have chosen to open:

  which is: application/octet-stream (6.0 KB)
  from: http://nn.nnn.nn.nnn
Would you like to save this file?
-----------------------------

Then performing the suggested workaround:

$ a2disconf serve-cgi-bin
Conf serve-cgi-bin disabled.
To activate the new configuration, you need to run:
  systemctl reload apache2
$ service apache2 restart

This brings up a BackupPC Server Status page.

In firefox, bringing up "http://10.208.83.246/backuppc/index.cgi?action=summary" then works as well.