Stream requestStream = null;
HttpWebRequest httpRequest = null;
try
{

            WebRequest webRequest = WebRequest.Create(url);
            httpRequest = webRequest as HttpWebRequest;
            if (httpRequest == null)
            {
                httpRequest.Abort();
                throw new ApplicationException(string.Format("无效的URL地址: {0}", url));
            }
            httpRequest.ContentType = "application/json";  //编码方式
            httpRequest.Method = "POST";  //提交方式
            httpRequest.ContentLength = data.Length;
            httpRequest.Accept = "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8";
            httpRequest.UserAgent = "Mozilla/5.0 (Windows; U; Windows NT 5.2; zh-CN; rv:1.9.2.8) Gecko/20100722 Firefox/3.6.8";
            

            httpRequest.Headers.Add("Authorization", "Basic " + contentType);
            httpRequest.CookieContainer = new CookieContainer();


            //httpRequest.ContentType = "application/json";
            requestStream = httpRequest.GetRequestStream();
            await requestStream.WriteAsync(data, 0, data.Length);

        }
        catch (Exception exx)
        {
            throw new Exception(string.Format("POST异常：{0}", exx.Message));

        }
        finally
        {
            if (requestStream != null) requestStream.Dispose();
        }

        Stream responseStream = null;
        HttpWebResponse res;
        byte[] b = null;
        MemoryStream ms = null;
        try
        {
            res = (HttpWebResponse)await httpRequest.GetResponseAsync();
            responseStream = res.GetResponseStream();

            ms = new MemoryStream();

            int count = 0;
            byte[] buff = new byte[1024];
            do
            {
                count = await responseStream.ReadAsync(buff, 0, buff.Length);
                ms.Write(buff, 0, count);

            } while (count > 0);
            b = ms.ToArray();
        }
        catch (WebException exp)
        {
            throw new Exception(string.Format("POST操作发生异常：{0}", exp.Message));
        }
        finally
        {
            if (ms != null) ms.Dispose();
            if (responseStream != null) responseStream.Dispose();
        }
        return b;

在Postman上可以访问，抓包查看header是没有一些参数，例如application/json抓包的时候header里就没有