add support for protected sites

https://docs.nginx.com/nginx/admin-guide/security-controls/configuring-subrequest-authentication/
https://gock.net/blog/2020/nginx-subrequest-authentication-server/
https://github.com/andygock/auth-server

src/server.js

@@ -20,7 +20,7 @@ let assert = require('assert'),
     users = require('./users.js'),
     ws = require('ws');
 
-var gHttpServer = null;
+let gHttpServer = null;
 
 function initializeExpressSync() {
     var app = express();
@@ -372,7 +372,7 @@ function stop(callback) {
     async.series([
         cloudron.uninitialize,
         database.uninitialize,
-        gHttpServer.close.bind(gHttpServer),
+        gHttpServer.close.bind(gHttpServer)
     ], function (error) {
         if (error) return callback(error);