user authentication libraries for node.js?

If you are looking for an authentication framework for Connect or Express, Passport is worth investigating: https://github.com/jaredhanson/passport

(Disclosure: I’m the developer of Passport)

I developed Passport after investigating both connect-auth and everyauth. While they are both great modules, they didn’t suit my needs. I wanted something that was more light-weight and unobtrusive.

Passport is broken down into separate modules, so you can choose to use only what you need (OAuth, only if necessary). Passport also does not mount any routes in your application, giving you the flexibility to decide when and where you want authentication, and hooks to control what happens when authentication succeeds or fails.

For example, here is the two-step process to setup form-based (username and password) authentication:

passport.use(new LocalStrategy(
  function(username, password, done) {
    // Find the user from your DB (MongoDB, CouchDB, other...)
    User.findOne({ username: username, password: password }, function (err, user) {
      done(err, user);
    });
  }
));

app.post('/login', 
  passport.authenticate('local', { failureRedirect: '/login' }),
  function(req, res) {
    // Authentication successful. Redirect home.
    res.redirect("https://stackoverflow.com/");
  });

Additional strategies are available for authentication via Facebook, Twitter, etc. Custom strategies can be plugged-in, if necessary.