Dropbox authentication with Node Express server

server.js

var express = require('express'),
    server = express(),
    events = require('events'),
    eventEmitter = new events.EventEmitter(),    
    Dropbox = require("dropbox"),

    options = {
      key: 'DROPBOX_KEY',
      secret: 'DROPBOX_SECRET'
    };

server.get('/auth', function (request, response) {

  // We need a new dropbox client for every user we authenticate
  var client = new Dropbox.Client(options);

  // Register a new authDriver
  client.authDriver({  

    // Not sure what this does
    authType: function() {return "code"},
    
    // Make sure you've registered the url below with Dropbox
    // as an OAUTH Redirect URI. Dropbox calls this once the user has agreed
    url: function() {return "http://localhost:8080/auth/callback"},
    
    doAuthorize: function(authUrl, stateParam, client, callback) {
      
      // Tell express to redirect the user to the correct authURL on dropbox.com
      response.redirect(authUrl);
    
      eventEmitter.once('auth_completed', function(state, code){

        if (state === stateParam) {return callback({code: code})}
          
      });    
    },
    
    oauthQueryParams: ['access_token', 'expires_in', 'scope', 'token_type', 'code', 'error', 'error_description', 'error_uri', 'mac_key', 'mac_algorithm'].sort()
  });
 
  client.authenticate(function(error, client) {
    
    if (error) {return console.log(error)}
    
    // Authenticated!
    doSomethingCool(client);
  });
 
});
 
server.get('/auth/callback', function(req, res){
  
  var code = req.query.code,
      state = req.query.state;

  eventEmitter.emit('auth_completed', state, code);
 
});
 
server.listen(8080);