How to fix missing strict transport security on OpenCart

Steps for OpenCart

1. OpenCart does not provide a built-in setting for HSTS headers — the header must be set at the server level.
2. For Apache: Edit your .htaccess file in the OpenCart root or your VirtualHost config for the HTTPS site. Add the HSTS Header directive from the Apache snippet below.
3. For Nginx: Add the add_header directive from the Nginx snippet below to your HTTPS server block, then reload Nginx.
4. Confirm in your OpenCart Admin → Settings → Server that 'Use SSL' is set to Yes for the entire store, not just checkout.
5. Verify with browser DevTools.

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.