code: func SetHeader(key, value string) func(next http.Handler) http.Handler {
  	return func(next http.Handler) http.Handler {
  		fn := func(w http.ResponseWriter, r *http.Request) {
  			w.Header().Set(key, value)
  			next.ServeHTTP(w, r)
  		}
  		return http.HandlerFunc(fn)
  	}
  }
docs: // SetHeader is a convenience handler to set a response header key/value