public void LuaPost(string url, Action<object,object,object> callback, string fields = null, bool isEncodFields = true, string header = null, int timeout = 5)
{
    StartCoroutine(_Post(url, delegate(long code, HttpHelperRequests requests, HttpHelperResponses rsponse)
    {
        callback?.Invoke(code, requests, rsponse);
    }, fields, isEncodFields, header, timeout));
}

IEnumerator _Post(string url, HttpHelperPostGetCallbacks callback, string fields, bool isEncodFields, string header, int timeout)
{
    using (UnityWebRequest webRequest = UnityWebRequest.Post(url, fields))
    {
        webRequest.timeout = timeout;
        //设置请求头  根据实际需求来
        webRequest.SetRequestHeader("Authorization", "");
        //处理请求头设置
        if (!string.IsNullOrEmpty(header))
        {
            JObject json = (JObject)Newtonsoft.Json.JsonConvert.DeserializeObject(header);
            if (json != null)
            {
                foreach (KeyValuePair<string, JToken> item in json)
                {
                    webRequest.SetRequestHeader(item.Key, item.Value.Value<string>());
                } 
            }
        }
        
        //不自动encode
        if (!string.IsNullOrEmpty(fields) && !isEncodFields)
        {
            byte[] bodyRaw = System.Text.Encoding.UTF8.GetBytes(fields);
            if (bodyRaw != null)
                webRequest.uploadHandler = new UploadHandlerRaw(bodyRaw);    
        }

        //开始与远程服务器通信
        //等待通行完成
        yield return webRequest.SendWebRequest();

        //组装请求信息
        HttpHelperRequests requests = new HttpHelperRequests();
        requests.url = url;
        requests.fileds = fields;
        requests.headers = header;

        //组装返回信息
        HttpHelperResponses responses = new HttpHelperResponses();
        responses.code = webRequest.responseCode;
        responses.message = webRequest.error;
        responses.headers = webRequest.GetResponseHeaders();
        responses.text = webRequest.downloadHandler.text;
        responses.bytes = webRequest.downloadHandler.data;

        //调用委托
        callback?.Invoke(webRequest.responseCode, requests, responses);

        //结束 处理占用资源
        //尽快停止UnityWebRequest
        webRequest.Abort();
        //默认值是true，调用该方法不需要设置Dispose()，Unity就会自动在完成后调用Dispose()释放资源。
        webRequest.disposeDownloadHandlerOnDispose = true;
        //不再使用此UnityWebRequest，并应清理它正在使用的任何资源
        webRequest.Dispose();
    }

}

注：请求体不使用encode，重新赋值webRequest.uploadHandler即可。有的服务器计算sing时可能用非encode的串计算