Node Cert Check

main.js

'use strict';

const tls = require('tls');

// HT: https://medium.com/@keithwan.programming/doing-ssl-certificate-expiry-alert-in-node-js-1714ef15621

const HOSTNAME = 'amazon.com';
const EXPIRATION_DAYS_THRESHOLD = 60;

function checkCertExpiry({ cert, days }) {
  const msDay = 24 * 3600 * 1000;
  const expiration = new Date(cert.valid_to).getTime();
  const threshold = Date.now() + days * msDay;
  const daysToExpiry = Math.floor((expiration - Date.now()) / msDay);
  const warn = expiration < threshold;
  return { expiration, threshold, daysToExpiry, warn };
}

const socket = tls.connect(
  {
    host: HOSTNAME,
    port: 443,
    servername: HOSTNAME,
  },
  () => {
    const peerCertificate = socket.getPeerCertificate({ detailed: true });
    const expiryObj = checkCertExpiry({
      cert: peerCertificate,
      days: EXPIRATION_DAYS_THRESHOLD,
    });

    // console.log(peerCertificate);

    const {
      issuer: { O },
      subject: { CN },
      serialNumber,
      subjectaltname,
    } = peerCertificate;
    // warn = CN.includes(HOSTNAME) || subjectaltname.includes(HOSTNAME);
    console.log({ O, CN, serialNumber, subjectaltname, ...expiryObj });
    socket.destroy();
  }
);
socket.on('error', (err) => {
  console.log('Error: ' + err.message);
});
socket.on('close', () => {});