NodeJS + Express: How to secure a URL

Yep, middleware is exactly what you want. A middleware function is just a function that works just like any other Express route handler, expept it gets run before your actual route handler. You could, for example, do something like this:

function requireLogin(req, res, next) {
  if (req.session.loggedIn) {
    next(); // allow the next route to run
  } else {
    // require the user to log in
    res.redirect("/login"); // or render a form, etc.
  }
}

// Automatically apply the `requireLogin` middleware to all
// routes starting with `/admin`
app.all("/admin/*", requireLogin, function(req, res, next) {
  next(); // if the middleware allowed us to get here,
          // just move on to the next route handler
});

app.get("/admin/posts", function(req, res) {
  // if we got here, the `app.all` call above has already
  // ensured that the user is logged in
});

You could specify requireLogin as a middleware to each of the routes you want to be protected, instead of using the app.all call with /admin/*, but doing it the way I show here ensures that you can’t accidentally forget to add it to any page that starts with /admin.