Node.js javascript example (#19)

* now with Javascript code

* navigation link fixed

* markdown fixed

README.md

@@ -3,6 +3,7 @@
 Tokens give you the ability to create URLs that expire. If you only want to give a particular user access to a link for a specific amount of time, you'll need tokens. They're commonly used to secure video assets, but you can create and validate signatures to be transferred in other ways, like cookies or authentication headers.
 
 #### Table of Contents
+
 - How to enable Token Authentication feature
   * [VCL](#vcl)
 - How to use
@@ -16,6 +17,7 @@ Tokens give you the ability to create URLs that expire. If you only want to give
   * [C#](#c)
   * [Java](#java)
   * [Rust](#rust)
+  * [Javascript (Node.js)](#javascript-nodejs)
 
 #### VCL
 
@@ -333,8 +335,31 @@ fn main() {
 }
 ```
 
+##### Javascript (Node.js)
+
+```javascript
+// a similar example can be tested and remixed at https://javascript-token-fastly.glitch.me/
+
+var crypto = require('crypto');
+
+var path = "/foo/bar.html";
+
+var base64Key = 'iqFPeN2u+Z0Lm5IrsKaOFKRqEU5Gw8ePtaEkHZWuD24=';
+// The Buffer.from method decodes a base-64 encoded string. 
+// Attention: don't convert key to a String or it may not work
+var key = Buffer.from(base64Key, 'base64');
 
+// 1,209,600 seconds = 2 weeks
+var token_lifetime = 1209600; 
+// Date.now() gives the current time with a millisecond precision
+var expiration = Math.round(Date.now()/1000 + token_lifetime);
 
+var string_to_sign = path + String(expiration);
 
+// calculate the token and convert to HEX
+var signature = crypto.createHmac('sha1', key).update(string_to_sign).digest('hex');
 
+var token = String(expiration) + "_" + signature;
 
+console.log("Token:", token); 
+```