This is not an official Google product.

Homebrew formula for Google Authenticator

Enables Google Authenticator as a two-factor authentication for Mac OS X ssh.

brew tap timothybasanov/google-authenticator
brew install google-authenticator
echo "auth required /usr/local/lib/security/pam_google_authenticator.so nullok" \
     | sudo tee -a /etc/pam.d/sshd
google-authenticator --force --time-based --disallow-reuse --rate-limit=3 \
     --rate-time=30 --window-size=10

See https://github.com/google/google-authenticator/tree/master/libpam for more information.

Caveat: As of August 2015 on Mac OS X El Capitan public beta clang crashes with a segfault. A workaround is to install brew install gcc. There is no pre-brewed bottle for El Capitan yet, installation can take hours. (see http://stackoverflow.com/questions/24966404/brew-install-gcc-too-time-consuming)