c# .net 4.0 HttpWebRequest 访问https TLS1.2 解决方案

ServicePointManager.SecurityProtocol = (SecurityProtocolType)3072;

public static string DoRequest(string Url, string cookieStr)
{
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(Url);

request.Timeout = 1000 *900;

request.Headers.Add(HttpRequestHeader.Cookie, cookieStr);

request.UserAgent = "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/31.0.1650.63 Safari/537.36";

ServicePointManager.SecurityProtocol = (SecurityProtocolType)3072;// SecurityProtocolType.Tls1.2;

string back ="";
try {
WebResponse response = request.GetResponse();
StreamReader reader = new StreamReader(response.GetResponseStream(), System.Text.Encoding.UTF8);
back = reader.ReadToEnd();
reader.Close();
reader.Dispose();
response.Close();
}
catch(Exception ex){

back = ex.Message;
}

return back;
}