Authentication 接口验证访问 (C#)

private HttpClient _httpClient = new HttpClient();

private string PostToOwner(CarOwnerCoupon postData)
        {
            string url ="www.abcxxxx.com";
            string base64Creds ="user" + ":" +"pwd";

            _httpClient.BaseAddress = new Uri(url);
            _httpClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue(
              "Basic", Convert.ToBase64String(Encoding.ASCII.GetBytes(base64Creds)));

            HttpContent content = new StringContent(JsonSerializer.Serialize(postData));
            content.Headers.ContentType = new MediaTypeHeaderValue("application/json");
            var result = _httpClient.PostAsync(url, content).Result.Content.ReadAsStringAsync().Result;
            return result;
        }