在APP首页：

if 没有登录 {

<script src="http://tjs.sjs.sinajs.cn/t35/apps/opent/js/frames/client.js" language="JavaScript"></script>
<script>
function authLoad() {
App.AuthDialog.show({
client_id: '2069027236', //必选，appkey
redirect_uri: 'http://apps.weibo.com/randytest', //必选，授权后的回调地址，注意是：apps.weibo.com这域名的
height: 1 //可选，默认距顶端120px
});
}
//authLoad();
</script>

}

然后会弹出一个登录的DIV,登录后会自动返回到app首页，然后在app page load的代码里写：

            string signedRequest = Request.Params["signed_request"]; 

            ViewBag.Message = ValidateSignedRequest(signedRequest);

 public string App_Secret = "xxxxxxxxxxxxxxxx";

        private string ValidateSignedRequest(string signedRequest)
        {
            string decodedPayload = "";
            string[] signedRequestArray = signedRequest.Split('.');
            string expectedSignature = signedRequestArray[0];
            string payload = signedRequestArray[signedRequestArray.Length - 1];
            byte[] Hmac = SignWithHmac(UTF8Encoding.UTF8.GetBytes(payload), UTF8Encoding.UTF8.GetBytes(App_Secret));
            string HmacBase64 = ToUrlBase64String(Hmac);
            bool result = (HmacBase64 == expectedSignature);
            if (result)
            {
                decodedPayload = System.Text.UTF8Encoding.UTF8.GetString(FromBase64ForUrlString(payload));
            }
            return decodedPayload;
        }
        private byte[] SignWithHmac(byte[] dataToSign, byte[] keyBody)
        {
            using (System.Security.Cryptography.HMACSHA256 hmacAlgorithm = new System.Security.Cryptography.HMACSHA256(keyBody))
            {
                hmacAlgorithm.ComputeHash(dataToSign);
                return hmacAlgorithm.Hash;
            }
        }
        private string ToUrlBase64String(byte[] Input)
        {
            return Convert.ToBase64String(Input).Replace("=", String.Empty).Replace('+', '-').Replace('/', '_');
        }
        private byte[] FromBase64ForUrlString(string base64ForUrlInput)
        {
            int padChars = (base64ForUrlInput.Length % 4) == 0 ? 0 : (4 - (base64ForUrlInput.Length % 4));
            StringBuilder result = new StringBuilder(base64ForUrlInput, base64ForUrlInput.Length + padChars);
            result.Append(String.Empty.PadRight(padChars, '=')).Replace('-', '+').Replace('_', '/');
            return Convert.FromBase64String(result.ToString());
        }

{"user":{"country":"cn","locale":""},"algorithm":"HMAC-SHA256","issued_at":1343130106,"expires":1343216506,"oauth_token":"2.00DBErpBCV7BQC169c3e7800XXXXX","user_id":1682372793,"referer":null}