Google is implementing 2-factor Authentication

http://links.f5.com/aAGhYQ

Your cell phone is the 2nd factor.

Regarding OAuth, here are some links to get you started.

http://links.f5.com/cmd7oJ

Twitter implemented it, but they asked developers not to put their keys in their application (and then allowed some important clients to exactly that)

http://links.f5.com/c3WLFN