I would like to make a request to an API using Postman. There is an example in the API documentation for Javascript using axios and crypto.

The documentation says the following

Signing a request The value of the X-App-Access-Sig is generated by a sha256 HMAC algorithm using a secret key (provided upon App Token generation) on the bytes obtained by concatenating the following information:

• A timestamp (value of the X-App-Access-Ts header) taken as a string
• An HTTP method name in upper-case, e.g. GET or POST
• URI of the request without a host name, starting with a slash and including all query parameters, e.g. /resources/applicants/123?fields=info
• Request body, taken exactly as it will be sent. If there is no request body, e.g., for GET requests, don't include it.

Example:

const axios = require('axios');
const crypto = require('crypto');

var config = {};
config.baseURL= BASE_URL;

axios.interceptors.request.use(createSignature, function (error) {
  return Promise.reject(error);
})

function createSignature(config) {
  console.log('Creating a signature for the request...');

  var ts = Math.floor(Date.now() / 1000);
  const signature = crypto.createHmac('sha256',  SECRET_KEY);
  signature.update(ts + config.method.toUpperCase() + config.url);

  if (config.data instanceof FormData) {
    signature.update (config.data.getBuffer());
  } else if (config.data) {
    signature.update (config.data);
  }

  config.headers['X-App-Access-Ts'] = ts;
  config.headers['X-App-Access-Sig'] = signature.digest('hex');

  return config;
}

My attempt to implement this as a postman Pre-request Script:

var CryptoJs = require("crypto-js")

console.log('Creating a signature for the request...');

const endpoint = pm.request.url.toString().split("{{BASE_URL}}").pop()
var ts = Math.floor(Date.now() / 1000);


const signature = CryptoJs.HmacSHA256(ts + pm.request.method.toUpperCase() + endpoint + pm.request.body, "{{SECRET_KEY}}")

pm.request.headers.add({
    key: 'X-App-Access-Ts',
    value: ts
})
pm.request.headers.add({
    key: 'X-App-Access-Sig',
    value: signature.toString(CryptoJs.enc.Hex)
})

console.log(pm.request)

But I get the error:

{
    "description": "Request signature mismatch",
    "code": 401,
    "correlationId": "req-53db2067-b0ec-4ce8-b333-387b0b20a955",
    "errorCode": 4003,
    "errorName": "app-token-signature mismatch"
}