feat: add sample multi-user support

feat: update README

api/server/routes/auth.js

@@ -0,0 +1,46 @@
+const express = require('express');
+const router = express.Router();
+const authYourLogin = require('./authYourLogin');
+const userSystemEnabled = process.env.ENABLE_USER_SYSTEM || false
+
+router.get('/login', function (req, res) {
+  if (userSystemEnabled)
+    res.redirect('/auth/your_login_page')
+  else
+    res.redirect('/')  
+})
+  
+router.get('/logout', function (req, res) {
+  // clear the session
+  req.session.user = null
+
+  req.session.save(function (error) {
+    if (userSystemEnabled)
+      res.redirect('/auth/your_login_page/logout')
+    else
+      res.redirect('/') 
+  })  
+})
+
+const authenticatedOr401 = (req, res, next) => {
+  if (userSystemEnabled) {
+    const user = req?.session?.user;
+
+    if (user) next();
+    else res.status(401).end();
+  } else next();
+}
+
+const authenticatedOrRedirect = (req, res, next) => {
+  if (userSystemEnabled) {
+    const user = req?.session?.user;
+
+    if (user) next();
+    else res.redirect('/auth/login').end();
+  } else next();
+}
+
+if (userSystemEnabled)
+  router.use('/your_login_page', authYourLogin);
+
+module.exports = { router, authenticatedOr401, authenticatedOrRedirect };