>> i've seen mention of a pam approach, but no detail yet..
>
> There are instructions on the site I linked to:
>
> http://code.google.com/p/google-authenticator/wiki/PamModuleInstructions

actually i meant/hoped for a pam approach to just key + password
enforcement.  in lieu of that, what i have seen so far is use
ForceCommand and a script to ask some question, it's not pam but
perhaps just as good.