Token authentication for Chef Server

Ping @smith @seth @mmzyk @danielsdeleo @lamont-granquist.

Hot off the presses, have at it!
I left them out because its a random string anyway so "base62" doesn't really hurt anything, and alphanumeric is less likely to conflict with anything while being a subset of the base64 charset. There is no standard for bearer tokens that I'm aware of, so I just picked something for the sake of being specific.