Golang リクエストのコンテキストをミドルウェアとハ​​ンドラーに渡すにはどうすればよいですか?

func checkAuth(authToken string) http.HandlerFunc {
  return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
    ctx := r.Context() // Retrieve the current context from the request

    if r.Header.Get("Auth") != authToken {
      util.SendError(w, "...", http.StatusForbidden, false)
      return
    }

    h := r.Context().Value(key) // Retrieve the handler from context
    h.ServeHTTP(w, r) // Pass the request to the handler
  })
}

func (h *HandlerW) ServeHTTP(w http.ResponseWriter, r *http.Request) {
  ctx := r.Context() // Retrieve the context from the request
  
  decoder := json.NewDecoder(r.Body)

  // Decode request / context and get params
  var p params
  err := decoder.Decode(&p)
  if err != nil {
    ...
    return
  }

  // Perform GET request and pass context
  ...

}

func main() {
  router := mux.NewRouter()

  // Initialize middleware handlers
  h := Handler{
    ...
  }

  // Pass context to authCheck
  authToken, ok := getAuthToken()
  if !ok {
    panic("...")
  }
  authCheck := checkAuth(authToken)

  // Chain middleware handlers and pass context
  router.Handle("/hello", util.UseMiddleware(authCheck, h, ...))
}