Creating JWT and signing it

Found this link and started with this:

var header = {
  "alg": "HS256",
  "typ": "JWT"
};

var data = {
  "id": 1337,
  "username": "john.doe"
};

var encodedHeader = btoa(JSON.stringify(header));
var encodedData = btoa(JSON.stringify(data));
var token = encodedHeader + "." + encodedData;
var secret = "My very confidential secret!";

print(token);

/* struggled at this point, no clue if there i an existing solution for this 
var signature = CryptoJS.HmacSHA256(token, secret);
*/

signature = btoa(signature);
var signedToken = token + "." + signature;

Any hints howto?