Setup Google Authenticator on FreeBSD

 Run as root:

cd /usr/ports/security/pam_google_authenticator
make install
mkdir /var/lib/google-authenticator

Edit /etc/pam.d/sshd:

auth      required    pam_google_authenticator.so nullok noskewadj

Edit /etc/pam.d/system:

auth      required    pam_google_authenticator.so nullok noskewadj

Leave out nullok if you do not want to allow users without having google-authenticator configured to be able to log in.
Be sure your root account has google-authenticator setup if you remove nullok and added it to /etc/pam.d/system.

Run google-authenticator with every user you want to be able to use it.

Source: https://www.schmidp.com/2014/01/12/setup-google-authenticator-on-freebsd/