Google Secure Access is a PPTP VPN that lets people bypass the insecure Wi-Fi link in a hotspot by wrapping their traffic in a tunnel.
Since PPTP and CHAP aren't that strong (and have been reported broken in a few occasions), Google has added client software that strengthens the login security by retrieving a one-time password from an SSL server (that seems to be about the only thing it does).
Resources:
- Google Secure Access on Mac OS X - retrieves the one-time password via curl and sets up the PPTP connection on Mac OS X.