Node PassportJS authentication: req.isAuthenticated() doesn't stay set - node.js

Question

Short summary of the problem: I'm using a new version of express (4.9.0) on a Node.js website which has a few public pages and a few private pages, which I'm putting behind a Google OAuth2 login, using PassportJS. When I request a page behind the sign-in, the user keeps being asked to sign-in; req.isAuthenticated() isn't "sticky". I've seen some comments online that there are can be problems with cookie parser versions being incompatible, so that could be the issue here.
Here is my (rather long) app.js:
var express = require('express');
var http = require('http');
var path = require('path');
var passport = require('passport');
var googleStrategy = require('passport-google-oauth').OAuth2Strategy;
var cookieParser = require('cookie-parser');
var bodyParser = require('body-parser');
var session = require('express-session');
var app = express();
app.use(cookieParser());
app.use(bodyParser());
app.use(session({ secret: 'mysecret' }));
app.set('view engine', 'html');
app.set('views', path.join(__dirname, 'views'));
app.engine('html', require('ejs').renderFile);
app.set('port', process.env.PORT || 3000);
app.use(passport.initialize());
app.use(passport.session());
passport.serializeUser(function(user, done) {
done(null, user);
});
passport.deserializeUser(function(obj, done) {
done(null, obj);
});
passport.use(new googleStrategy({
clientID: clientId,
clientSecret: secret,
callbackURL: "http://127.0.0.1:3000/auth/google/callback"
},
function (accessToken, refreshToken, profile, done) {
process.nextTick(function () {
return done(null, profile);
});
}
));
app.get('/auth/google',
passport.authenticate('google', { scope: ['https://www.googleapis.com/auth/userinfo.profile',
'https://www.googleapis.com/auth/userinfo.email'] }),
function(req, res){
});
app.get('/auth/google/callback',
passport.authenticate('google', { failureRedirect: '/login' }),
function(req, res) {
console.log("successfully authenticated with google");
res.redirect('/');
});
app.get('/login', function(req, res){
res.redirect('/auth/google');
});
app.get('/privatepage', ensureAuthenticated, function(req, res) {
var dostuff = module.listThings(function(rows) {
res.render('somepage.html', {
title : "some page",
data : rows
});
});
});
function ensureAuthenticated(req, res, next) {
console.log("in ensureAuth", req.isAuthenticated());
console.log("session data", req.session);
console.log("user data", req.user);
if (req.isAuthenticated()) { return next(); }
res.redirect('/login');
}
var server = app.listen(3000, function() {
var host = server.address().address
var port = server.address().port
console.log('App listening at http://%s:%s', host, port)
})
After the first login, if I visit the /privatepage URL, I get re-directed through Google and land on the homepage again. This is what's in the log from those console.log lines:
in ensureAuth false
session data { cookie:
{ path: '/',
_expires: null,
originalMaxAge: null,
httpOnly: true },
passport: {} }
user data undefined
I assume this is some session issue where it doesn't store the user's logged in state, but I'm a node newbie & am a little stuck on how to fix this. I'm running on a single computer, so it's not a multiple machines issue. Any debugging suggestions, or ideas on the conflict causing the logged-in state not to be stored?