How to fix missing strict transport security on Headless / Custom (I build in code)

Steps for Headless / Custom (I build in code)

1. Add the Strict-Transport-Security response header inside your server or middleware layer — see the code snippets below for Node.js (Express), Next.js, and generic server config formats.
2. For Next.js: Add the header in next.config.js under the headers() async function.
3. For Express.js: Use the helmet npm package (helmet() includes HSTS by default) or set the header manually with res.setHeader().
4. For any reverse proxy (Nginx, Apache, Caddy) in front of your application: add the header at the proxy level so it applies to every response regardless of the backend.
5. Set max-age=31536000 (one year) and includeSubDomains. Test with browser DevTools before enabling preload.
6. After deploying, verify with securityheaders.com or hstspreload.org.

What is missing strict transport security?

HTTP Strict Transport Security (HSTS) is a small instruction your web server sends inside every page response that tells browsers: "never load this site over plain HTTP — always use HTTPS, no exceptions." Without it, a browser will happily follow any link or redirect that starts with `http://`, even if your server immediately redirects to `https://`. That brief unencrypted moment is enough for an attacker on the same Wi-Fi network to intercept the request. The HSTS header closes that window entirely by making the browser refuse the insecure connection before it even leaves the device.

Security: Customers shopping on public Wi-Fi are vulnerable to SSL-stripping attacks — where a hacker silently downgrades their HTTPS session to plain HTTP and reads login cookies, payment info, or session tokens in the clear. HSTS prevents this. *SEO & Rankings:* Google uses HTTPS as a confirmed ranking signal and may deprioritize pages that can be reached over HTTP; a strong HSTS policy reinforces your site's "always-HTTPS" status. *Compliance & Legal:* PCI-DSS (required for any store that handles card payments) and GDPR both demand that customer data be encrypted in transit — a missing HSTS header is a finding auditors flag. *Conversions:* Browsers display security warnings for mixed-content or downgrade scenarios; even a brief warning causes visitors to abandon their cart.

See the complete Missing strict transport security guide for every platform and the full background.