Are you using node.js for the whole stack? Or is there a Rails app running alongside for doing user accounts, payments, the marketing site/landing page etc?
It's all built on node.js. We used rails before to handle user accounts and static pages but realized we could make it all with node.js and MongoDB instead with some cool template language. :)
We've built a lot on our own. Maybe Senchalabs Connect can help you, otherwise check https://github.com/joyent/node/wiki/modules. Don't know if it's better than devise/cancan though.