Packages to install:

yum install -y google-authenticator freeradius freeradius-utils

/etc/raddb/radiusd.conf:

Unfortunately radiusd needs to be running as root to utilize PAM?

user = root
group = root

/etc/pam.d/radiusd:

This seems to be working so far.

auth required pam_google_authenticator.so debug forward_pass
auth required pam_unix.so debug use_first_pass
#auth required pam_unix.so debug
account required        pam_unix.so

/etc/raddb/users:

Add the first DEFAULT line above the second.

DEFAULT Auth-Type := PAM

DEFAULT Framed-Protocol == PPP
        Framed-Protocol = PPP,
        Framed-Compression = Van-Jacobson-TCP-IP