I've created a repo for my side project on "JSON Web Tokens in Javascript". The JSON Web Tokens (JWT) spec defines a way to digitally sign JSON blobs so they can be relayed between parties, through the browser or server-to-server.
The repo is at:
https://github.com/michaelrhanson/jwt-js
The code is quite incomplete; it only supports the sign() operation for HMAC-SHA256 and RSA-SHA256 right now. Updates to come.
m