starling-auth.js

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

const pem = fs.readFileSync('./pem.pem', 'utf8')

const sha = crypto.createHash('sha512');
sha.update(JSON.stringify({"item": "test"}));
const digest = sha.digest('base64');

const url = 'put /api/v1';
const date = new Date(); // this is the wrong format

const headers = `(request-target): ${url} Date: ${date} Digest: ${digest || 'X'}`

const sign = crypto.createSign('rsa-sha256');
sign.update(headers);
sign.end();

const signature = sign.sign(pem, 'base64');

const UUID = 1234;

const Authorization = `Bearer ""; Signature keyid="${UUID}",algorithm="rsa-sha256",headers="${headers}",signature="${signature}"`;

console.log(Authorization);