Implementing HTTP Strict Transport Security (HSTS)

Introduction

HTTP Strict Transport Security (HSTS) is a web security policy mechanism that helps to protect websites against man-in-the-middle attacks such as protocol downgrade attacks and cookie hijacking.

When a server sends the Strict-Transport-Security header, it tells the browser that for a specified period of time, the browser must only communicate with the server over HTTPS, even if the user manually types http:// in the URL bar.

Implementing HSTS with Helmet

The easiest and safest way to implement HSTS in an Express application is by using the helmet middleware.

npm install helmet

const express = require('express');
const helmet = require('helmet');

const app = express();

// Helmet automatically enables HSTS along with other security headers
app.use(helmet());

Manual Configuration

If you want to configure HSTS explicitly or without Helmet, you can use the helmet.hsts middleware specifically:

const express = require('express');
const helmet = require('helmet');

const app = express();

const sixtyDaysInSeconds = 5184000;

app.use(helmet.hsts({
  maxAge: sixtyDaysInSeconds,
  includeSubDomains: true, // Apply to all subdomains
  preload: true            // Allow submission to Chrome's HSTS preload list
}));

Warning

HSTS is extremely powerful, but dangerous if misconfigured. If you deploy HSTS with a long maxAge and your SSL certificate expires or you lose control of your HTTPS infrastructure, your users will be completely locked out of your site until the maxAge expires! Always start with a small maxAge (e.g., a few minutes) to test your configuration before rolling it out with a year-long expiration.

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