Fastify

HSTS is one of those headers that’s dead simple on paper and weirdly easy to mess up in production. If you run a TypeScript app with tRPC, you usually don’t “add HSTS to tRPC” directly. You add it at the HTTP layer that serves your tRPC endpoint: Express, Fastify, Next.js custom server, Nginx, your edge platform, or your CDN. That distinction matters because if you set it in the wrong place, your API might still be exposed over plain HTTP during redirects or on subdomains you forgot existed. ...

HSTS looks simple: send one response header and browsers stop talking to your site over plain HTTP. The catch is that HSTS is one of those headers that can absolutely improve security and absolutely break things if you roll it out carelessly. I’ve seen teams flip on includeSubDomains in production and then spend the afternoon finding forgotten subdomains, old staging boxes, and random vendor callbacks still using HTTP. If you’re running Fastify, you’ve got a few ways to handle HSTS: ...