HSTS for Server-Sent Events: A Production Fix

A lot of teams treat Server-Sent Events like “just another endpoint.” That’s how you end up with a perfectly secure app shell over HTTPS and a quietly fragile event stream still hanging onto old HTTP assumptions. I’ve seen this play out in production: the page loads fine, login works, API calls are on HTTPS, HSTS is enabled on the main site, and yet live updates randomly fail, especially after deploys, browser restarts, or when users hit older bookmarked URLs. The culprit was SSE over an incomplete HTTPS setup. ...

September 6, 2026 · 7 min · headertest.com