[mryan]

Seconding the recommendation for PAM/Google Authenticator.

Off-topic: Has anyone ever managed to get PAM/Google Authenticator working with RADIUS? I spent a while messing about with this last year, and never got it working exactly as I had hoped. I'm no longer working with RADIUS, but this post reminded me I never finished scratching that geeky itch.

[bithive123]

I wrote a Sinatra app to act as a Google Authenticator backend for our FreeRADIUS instance as well as our web SSO. It also handles enrollment via generating QR codes:

http://it.isevil.org/blog/2011/11/13/authentication-service-...

Code: https://github.com/bithive/example-totp-vault

For FreeRADIUS we use rlm_perl to define our own authenticate() method; it just calls the web service to validate the codes.

[mryan]

Neat solution, thanks for sharing.

[seanponeil]

I can't speak for Google Authenticator but Duo works great with RADIUS http://www.duosecurity.com/docs/radius