apache2 won't restart after installing nagios4

[gregrwm]

the issue is described here: https://wiki.debian.org/Nagios4

in summary, after installing nagios4, apache2 won't restart, until:

a2enmod auth_digest
a2enmod authz_groupfile

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: nagios4 (not installed)
ProcVersionSignature: Ubuntu 5.4.0-42.46-generic 5.4.44
Uname: Linux 5.4.0-42-generic x86_64
ApportVersion: 2.20.11-0ubuntu27.4
Architecture: amd64
CasperMD5CheckResult: pass
Date: Thu Apr 29 21:33:16 2021
InstallationDate: Installed on 2020-11-30 (150 days ago)
InstallationMedia: Ubuntu-Server 20.04.1 LTS "Focal Fossa" - Release amd64 (20200731)
ProcEnviron:
 TERM=screen
 PATH=(custom, no user)
 LANG=C.UTF-8
 SHELL=/bin/bash
SourcePackage: nagios4
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.