middleware/value.go
func WithValue(key interface{}, val interface{}) func(next http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		fn := func(w http.ResponseWriter, r *http.Request) {
			r = r.WithContext(context.WithValue(r.Context(), key, val))
			next.ServeHTTP(w, r)
		}
		return http.HandlerFunc(fn)
	}
}
func WithValue(key interface{}, val interface{}) func(next http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		fn := func(w http.ResponseWriter, r *http.Request) {
			r = r.WithContext(context.WithValue(r.Context(), key, val))
			next.ServeHTTP(w, r)
		}
		return http.HandlerFunc(fn)
	}
}
// WithValue is a middleware that sets a given key/value in a context chain.