Helping http://stackoverflow.com/q/21830918/804100

app.js

var express = require('express');

var app = express();

app.all('*', function(req, res, next) {
	var youAreAllowed = Math.random() < 0.5; // example
	if (youAreAllowed)
		next();
	else
		res.send(403);
});

// By the way:
// You might want the above thing to be middleware if it handles EVERYTHING.
// Looks very similar, but the first line looks like this:
// app.use(function(req, res, next) {
//   ..

app.get('/', function(req, res) {
	res.send('hello world!');
});

app.listen(8000);