Add Duo Two-Factor auth to SSH in Ubuntu

Duo offers a relatively simple way to add support Duo two-factor auth to SSH sessions in multiple Linux Distributions. Here are my steps for Ubuntu Server.

1. Create /etc/apt/sources.list.d/duosecurity.list with the following contents:
deb [arch=amd64] https://pkg.duosecurity.com/Ubuntu focal main
2. Create a user that corresponds to your username in Duo.
3. Create admin group in Ubuntu.
   # groupadd admin
4. Add your user to admin group (Ubuntu) or wheel group (RedHat)
   # usermod -G admin username
5. Install the Duo package either from source or repo. Here we will install it from the Duo repo.
   # curl -s https://duo.com/DUO-GPG-PUBLIC-KEY.asc | sudo apt-key add -
# apt update && apt install duo-unix
6. Enable duo in by adding the following line in /etc/ssh/sshd_config:
   ForceCommand /usr/sbin/login_duo
7. Restard sshd.
   # systemctl restart sshd
8. Add Duo keys to /etc/duo/login_duo.conf. These keys are provided by Duo when you create an application.
9. Change ownership of /etc/duo/login_duo.conf using the following command.
   # chown sshd.root /etc/duo/login_duo.conf
10. Test the integration by using a separate ssh session to login to the system you just installed Duo on.