code: func hstsHandler(fn http.HandlerFunc) http.Handler {
  	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
  		w.Header().Set("Strict-Transport-Security", "max-age=31536000; preload")
  		fn(w, r)
  	})
  }
docs: // hstsHandler wraps an http.HandlerFunc such that it sets the HSTS header.