解决https 请求过程中SSL问题

最近一个项目中用到了https的请求，在实际调用过程中发现之前的http方法不支持https，调用一直报错。

查询了一下，添加几行代码解决问题。

 public string httppost(string url, string postdatastr, string useragent = null)
        {
            servicepointmanager.servercertificatevalidationcallback += (s, cert, chain, sslpolicyerrors) => true;//新增一行
            system.net.servicepointmanager.securityprotocol = (securityprotocoltype)192 | (securityprotocoltype)768 | (securityprotocoltype)3072;//新增第二行，很重要
            servicepointmanager.servercertificatevalidationcallback = new system.net.security.remotecertificatevalidationcallback(checkvalidationresult);//新增第三行
            httpwebrequest request = (httpwebrequest)webrequest.create(url);
            request.method = "post";
            request.contenttype = "application/x-www-form-urlencoded";
            request.contentlength = encoding.utf8.getbytecount(postdatastr);
            if (!string.isnullorempty(useragent))
            {
                request.useragent = useragent;
            }
            stream myrequeststream = request.getrequeststream();
            streamwriter mystreamwriter = new streamwriter(myrequeststream, encoding.getencoding("gb2312"));
            mystreamwriter.write(postdatastr);
            mystreamwriter.close();

            httpwebresponse response = (httpwebresponse)request.getresponse();


            stream myresponsestream = response.getresponsestream();
            streamreader mystreamreader = new streamreader(myresponsestream, encoding.getencoding("utf-8"));
            string retstring = mystreamreader.readtoend();
            mystreamreader.close();
            myresponsestream.close();

            return retstring;
        }