JWT

const crypto = require('crypto');

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

let body = {
  "sub": "1234567890",
  "name": "John Doe",
  "iat": 1516239022
}

function removePadding(base64) {
    return base64.split("=").join("");
}

function toBase64(string) {
    return Buffer.from(string).toString("base64");
}

function process(body, header, key) {
    var contents = removePadding(toBase64(JSON.stringify(header))) + "." + removePadding(toBase64(JSON.stringify(body)))
    var hmac = crypto.createHmac('sha256',  key);
    hmac.update(contents);
    contents  += "." + removePadding(hmac.digest('base64'));
    return contents;
}

let jwt = process(body, header, 'ffffffddfd');
console.log(jwt)