How to Generate JWT Signature (HS256) in Node.js

August 11, 2022

How to create JWT Signature using HS256 algorithm in Node.js?

I’ll be using it to generate digital signature required for every request in here BNI API

>Solution :

To generate JWT Signature in HS256 to be use for digital signature in BNI API you must convert payload to base64URL first, try this code

// convert to JWT base64URL
const escape = (string) => {
  return string.replace(/\+/g, '-').replace(/\//g, '_').replace(/=/g, '');
};

const generateSignature = (body, secret) => {
  // generate JWT header
  const header = escape(Buffer.from('{"alg":"HS256","typ":"JWT"}').toString('base64'));

  // generate JWT payload
  const payload = escape(Buffer.from(JSON.stringify(body)).toString('base64'));

  // generate JWT signature
  const jwtSignature = crypto.createHmac('SHA256', secret).update(`${header}.${payload}`).digest('base64');

  // return generated JWT token
  return escape(`${header}.${payload}.${jwtSignature}`);
}