Android SDK 6.8.20版本中，使用 sendReq 分享网页内容时，

具体如何在服务端，利用开放平台生成的私钥，去生成签名，添加签名，以实现防篡改校验？签名应放在哪个参数中？是否有示例代码？

比如如下代码，在我分享时，被篡改了webpageUrl，导致点击分享卡片时，打开的链接是篡改后的链接，我要怎么添加代码？

WXWebpageObject webpage = new WXWebpageObject();

webpage.webpageUrl = "http://www.qq.com";

WXMediaMessage msg = new WXMediaMessage(webpage);

msg.title = "WebPage Title WebPage Title WebPage Title WebPage Title WebPage Title WebPage Title WebPage Title WebPage Title WebPage Title Very Long Very Long Very Long Very Long Very Long Very Long Very Long Very Long Very Long Very Long";

msg.description = "WebPage Description WebPage Description WebPage Description WebPage Description WebPage Description WebPage Description WebPage Description WebPage Description WebPage Description Very Long Very Long Very Long Very Long Very Long Very Long Very Long";

Bitmap bmp = BitmapFactory.decodeResource(getResources(), R.drawable.send_img);

Bitmap thumbBmp = Bitmap.createScaledBitmap(bmp, THUMB_SIZE, THUMB_SIZE, true);

bmp.recycle();

msg.thumbData = Util.bmpToByteArray(thumbBmp, true);

SendMessageToWX.Req req = new SendMessageToWX.Req();

req.transaction = buildTransaction("webpage");

req.message = msg;

req.scene = mTargetScene;

api.sendReq(req);

1.为什么我 已开启全部API加密及签名校验，但是无论是否添加签名，微信分享还是能正常分享。

2.appid、description、thumbDataHash、title、webpageUrl这几个字段是必须要签名的吗，比如我只需要签名webpageUrl可以吗