auth.js

var passport = require('passport'),
    TwitterStrategy = require('passport-twitter').Strategy,
    GoogleStrategy = require('passport-google-oauth').Strategy,
    users = require('./model').users;
    
/*
This is for serializing a user object.
Basically, it should return all of an user object
that is necessary to identify it. Usually, the id
field will do just fine.
*/
passport.serializeUser(function(user, done) {
  done(null, user.id);
});

/*
This goes the other way around. This function should
return a full user object. This is not only database agnostic,
you can also use web services or whatever here.
*/
passport.deserializeUser(function(id, done) {
  users.findOne({id: id}, done);
});

var findOrCreate = function(provider, id, name, done) {
  users.findOne({"auth.provider": provider, "auth.id": profile.id}, function(err, user) {
    if(err || user) done(err, user);
    else {
      user = {auth: [{provider: provider, id: id}], name: profile.name };
      users.insert(user, {safe: true}, function(err, usrs) {
        done(err, usrs[0]);
      });
    }
  });
}

passport.use(new TwitterStrategy(
  {
    consumerKey: process.env.TWITTER_CONSUMER_KEY,
    consumerSecret: process.env.TWITTER_CONSUMER_SECRET,
    callbackURL: "http://" + process.env.domain + "/auth/twitter/callback"
  }, function(token, tokenSecret, profile, done) {
    findOrCreate('twitter', profile.id, profile.name, done);
}));

passport.use(new GoogleStrategy(
  {
    clientID: process.env.GOOGLE_CLIENT_ID,
    clientSecret: process.env.GOOGLE_CLIENT_SECRET,
    callbackURL: "http://" + process.env.domain + "/auth/google/callback"
  }, function(accessToken, refreshToken, profile, done) {
    findOrCreate('google', profile.id, profile.name, done);
}));

module.exports.setup = function(app) {
  app.get('/auth/twitter', passport.authenticate('twitter')));
  app.get('/auth/google', passport.authenticate('google', scope: {'https://www.googleapis.com/auth/userinfo.profile'})));
  
  app.get('/auth/twitter/callback', passport.authenticate('twitter', {successRedirect: '/', failureRedirect: '/login'})));
  app.get('/auth/google/callback', passport.authenticate('google', {successRedirect: '/', failureRedirect: '/login'})));
}

module.exports.authenticationRequired = function(req, res, next) {
  if(req.isAuthenticated()) next();
  else res.redirect('/login');
}

module.exports.logout = function(req, res) {
  req.logOut();
  res.redirect('/login');
}