BetterPHP

I'm creating an app in NodeJS with Express (not the important part) and I'm wondering how I would go about with having a single-sign on without password? I'm not talking code wise, but structure wise, what would I want to do to keep this secure?

Use OpenID to manage single sign-on.
I'm not too sure how to about doing this, but I think this will get you on the right track (maybe).

http://openid.net/add-openid/add-getting-started/