Extract JSON object from https://smarthealth.cards QR code

shc2.js

// modified by joedf from https://gist.github.com/remi/e3aa2f78845ee13f706ed83aead5145f
// Extract JSON payload from SHC QR code (without any kind of private/public key verification)

// Credits + inspiration
// https://github.com/dvci/health-cards-walkthrough/blob/main/SMART%20Health%20Cards.ipynb

// Usage
// $ node shc2.js "shc:/01234569…"

const zlib = require("zlib");

// Extract the QR data from arguments
const data = process.argv[2];

// Convert the data to a JWT and extract its base64-encode payload
const jwt = data
  .split("/")[1]
  .match(/(..?)/g)
  .map((number) => String.fromCharCode(parseInt(number, 10) + 45))
  .join("")
  .split(".");

const header = jwt[0];
const payload = jwt[1];
const secret = jwt[2];

console.log('\nHeader: ', decode_JWT(header,1));
console.log('\nPayload: ', decode_JWT(payload));
console.log('\nSecret: ', decode_JWT(secret,2));

function decode_JWT(data, mode=0) {
  // Decode the data
  const buffer = Buffer.from(data, "base64");

  var ret;

  switch(mode)
  {
    case 0: // Uncompress the data and return the result
      ret = prettyJson(zlib.inflateRawSync(buffer).toString("utf8")); break;

    case 1: ret = prettyJson(buffer.toString("utf8")); break;

    default: ret = data;
  }

  return ret;
}

function prettyJson(s) { return JSON.stringify(JSON.parse(s), null, 4); }