Twitter OAuth with node-oauth for node.js+express

server.js

var express = require('express');
var sys = require('sys');
var oauth = require('oauth');

var app = express.createServer();

var _twitterConsumerKey = "YOURTWITTERCONSUMERKEY";
var _twitterConsumerSecret = "YOURTWITTERCONSUMERSECRET";

function consumer() {
  return new oauth.OAuth(
    "https://twitter.com/oauth/request_token", "https://twitter.com/oauth/access_token", 
    _twitterConsumerKey, _twitterConsumerSecret, "1.0A", "http://badgestar.com/sessions/callback", "HMAC-SHA1");   
}

app.configure('development', function(){
  app.use(express.errorHandler({ dumpExceptions: true, showStack: true }));
  app.use(express.logger());
  app.use(express.cookieDecoder());
  app.use(express.session());
});

app.dynamicHelpers({
  session: function(req, res){
    return req.session;
  }
});

app.get('/', function(req, res){
  res.send('Hello World');
});

app.get('/sessions/connect', function(req, res){
  consumer().getOAuthRequestToken(function(error, oauthToken, oauthTokenSecret, results){
    if (error) {
      res.send("Error getting OAuth request token : " + sys.inspect(error), 500);
    } else {  
      req.session.oauthRequestToken = oauthToken;
      req.session.oauthRequestTokenSecret = oauthTokenSecret;
      res.redirect("https://twitter.com/oauth/authorize?oauth_token="+req.session.oauthRequestToken);      
    }
  });
});

app.get('/sessions/callback', function(req, res){
  sys.puts(">>"+req.session.oauthRequestToken);
  sys.puts(">>"+req.session.oauthRequestTokenSecret);
  sys.puts(">>"+req.query.oauth_verifier);
  consumer().getOAuthAccessToken(req.session.oauthRequestToken, req.session.oauthRequestTokenSecret, req.query.oauth_verifier, function(error, oauthAccessToken, oauthAccessTokenSecret, results) {
    if (error) {
      res.send("Error getting OAuth access token : " + sys.inspect(error) + "["+oauthAccessToken+"]"+ "["+oauthAccessTokenSecret+"]"+ "["+sys.inspect(results)+"]", 500);
    } else {
      req.session.oauthAccessToken = oauthAccessToken;
      req.session.oauthAccessTokenSecret = oauthAccessTokenSecret;
      // Right here is where we would write out some nice user stuff
      consumer.get("http://twitter.com/account/verify_credentials.json", req.session.oauthAccessToken, req.session.oauthAccessTokenSecret, function (error, data, response) {
        if (error) {
          res.send("Error getting twitter screen name : " + sys.inspect(error), 500);
        } else {
          req.session.twitterScreenName = data["screen_name"];    
          res.send('You are signed in: ' + req.session.twitterScreenName)
        }  
      });  
    }
  });
});

app.listen(parseInt(process.env.PORT || 80));

TypeError: Cannot set properties of undefined (setting 'oauthRequestToken')