c#:HttpClient加標頭

using (var client = new HttpClient())
{
string requestUrl = string.Format("{0}{1}", ConstDefine.Host, "api/XXXX/");
client.DefaultRequestHeaders.Add("Accept", "application/json");//加頭
HttpResponseMessage response = await client.PostAsJsonAsync(requestUrl, 數據);
response.EnsureSuccessStatusCode();
string rect = await response.Content.ReadAsStringAsync();
apiRect = JsonConvert.DeserializeObject<RetModel<string>>(rect);
}