Add optional secret to websocket communication

[dafenix]

This change allows you to specify a secret that is checked when establishing a WebSocket connection. With this change, a client can only establish a connection if it specifies the correct secret. If no secret is specified, the application behaves as before.

How to test.

• Start server npm run build && bin/chii.js start --secrets 333,444
• Connect to it

With valid secret:

(function () {
 var script = document.createElement('script');
 script.type = 'text/javascript';
 script.src = 'http://localhost:8080/target.js'; 
 script.setAttribute('secret', '333');
 document.getElementsByTagName('head')[0].appendChild(script);
})();

(function () {
 var script = document.createElement('script');
 script.type = 'text/javascript';
 script.src = 'http://localhost:8080/target.js'; 
 script.setAttribute('secret', '444');
 document.getElementsByTagName('head')[0].appendChild(script);
})();

With invalid secret:

(function () {
 var script = document.createElement('script');
 script.type = 'text/javascript';
 script.src = 'http://localhost:8080/target.js'; 
 script.setAttribute('secret', '999');
 document.getElementsByTagName('head')[0].appendChild(script);
})();

With no secret:

(function () {
 var script = document.createElement('script');
 script.type = 'text/javascript';
 script.src = 'http://localhost:8080/target.js'; 
 document.getElementsByTagName('head')[0].appendChild(script);
})();

[dafenix]

@surunzi