req.user undefined - node + express + passport-facebook

Question

i'm trying to get passport to work with my node express server. I can login in with Facebook and find the correct user in my database; however, when I redirect req.user is always undefined. Here is my server code:

var express = require('express'),
path = require('path'),
http = require('http'),
passport = require('passport'),
FacebookStrategy = require('passport-facebook').Strategy,
user = require('./routes/users');


var app = express();

passport.use(new FacebookStrategy({
    clientID: "HIDDEN",
    clientSecret: "HIDDEN",
    callbackURL: "http://MYURL.com/auth/facebook/callback",
    passReqToCallback: true
 },
  function(req, accessToken, refreshToken, profile, done) {
    user.findOrCreate(profile, function(err, user) {      
      if (err) { return done(err); }      
      done(null, user);
    });    
  }
));

passport.serializeUser(function(user, done) {  
  done(null, user._id);
});

passport.deserializeUser(function(id, done) {
  user.findById(id, function(err, user) {
    done(err, user);
  });
});

app.configure(function () {    
app.set('port', process.env.PORT || 3000);
    app.use(express.static(path.join(__dirname, 'public')));
    app.use(express.logger('dev')); /* 'default', 'short', 'tiny', 'dev' */
    app.use(express.bodyParser());
    app.use(express.cookieParser());
    app.use(express.session({ secret: 'foobar' }));   
    app.use(passport.initialize());
    app.use(passport.session()); 
    app.use(app.router);    
});

app.get('/auth/user', function (req, res) {
    console.log(req);
});

app.get('/auth/facebook', passport.authenticate('facebook'));
app.get('/auth/facebook/callback', 
  passport.authenticate('facebook', { successRedirect: '/',
                                      failureRedirect: '/login' }));


http.createServer(app).listen(app.get('port'), function () {
    console.log("Express server listening on port " + app.get('port'));
});

I go to /auth/facebook, it finds the correct user and redirects me to /. But then I go to /auth/user and req.user is undefined and my sessions show this:

cookies: { 'connect.sid': 's:JFdQkihKQQyR4q70q7h2zWFt.VS+te0pT0z/Gtwg7w5B33naCvA/ckKMk60SFenObxUU' },
  signedCookies: {},
  url: '/auth/user',
  method: 'GET',
  sessionStore:
   { sessions:
      { '5sk3Txa2vs5sYhvtdYwGaUZx': '{"cookie":{"originalMaxAge":null,"expires":null,"httpOnly":true,"path":"/"},"passport":{"user":"50c527c9c6cb41860b000001"}}',
        'Au6m0hAj/3warKOGNSWw0yu2': '{"cookie":{"originalMaxAge":null,"expires":null,"httpOnly":true,"path":"/"},"passport":{}}',
        JFdQkihKQQyR4q70q7h2zWFt: '{"cookie":{"originalMaxAge":null,"expires":null,"httpOnly":true,"path":"/"},"passport":{}}' },
     generate: [Function],
     _events: { disconnect: [Function], connect: [Function] } },
  sessionID: 'JFdQkihKQQyR4q70q7h2zWFt',

Does it have something to do with my sessionID not matching the session where the passport user is set?

Update

So I determined that the sessionID not matching was because I'm running my code on c9.io and it actually has two URLs. When I use the correct URL and go to /auth/user my sessionID matches the session with passport user set and I can see in the log my deserializeUser finding the correct user object. However, req.user is still undefined after this.

Trying to find user with id: 50c527c9c6cb41860b000001
{ sessions:
   { yoOUOxyXZ0SmutA0t5xUr6nI: '{"cookie":{"originalMaxAge":null,"expires":null,"httpOnly":true,"path":"/"},"passport":{"user":"50c527c9c6cb41860b000001"}}',
     goZpmK3y3tOfn660hRbz2hSa: '{"cookie":{"originalMaxAge":null,"expires":null,"httpOnly":true,"path":"/"},"passport":{}}',
     'O5Sz1GuZqUO8aOw4Vm/hriuC': '{"cookie":{"originalMaxAge":null,"expires":null,"httpOnly":true,"path":"/"},"passport":{}}' },
  generate: [Function],
  _events: { disconnect: [Function], connect: [Function] } }
sessionID: yoOUOxyXZ0SmutA0t5xUr6nI
req.user: undefined
{ cookie:
   { path: '/',
     _expires: null,
     originalMaxAge: null,
     httpOnly: true },
  passport: {} }

Update2

I figured out the problem. It was in my user.findByID function:

exports.findById = function(id, callback) {    
    console.log('Trying to find user with id: ' + id);
    db.collection('users').findOne({'_id':id}, function(err, user) {           
            callback(err, user);
    });
};

changed to:

exports.findById = function(id, callback) {    
    console.log('Trying to find user with id: ' + id);
    db.collection('users').findOne({'_id':new BSON.ObjectID(id)}, function(err, user) {           
            callback(err, user);
    });
};

Answer 1

As you said in you update it was the user._id variable not being in a valid format. To avoid this and having to take care of this format later in other requests and methods I will advice you to generate a new user id at signup.

You can use this module:

node-uuid

var uuid = require('node-uuid');

function findOrCreate(profile, callback) {
  // save new profile
  profile.uid = uuid.v1().replace(/\-/g, '');
}