C# SAML-2无法创建HTTP-REDIRECT绑定签名URL参数

据我所知，如果我想签署SAML请求，签名应该由以下内容构成：

SAMLRequest=VALUE&RelayState=VALUE&SigAlg=VALUE 因此我应该创建签名，这是我用来创建签名的一段代码：

var MSCert = new X509Certificate2(ConfigurationManager.AppSettings["KeyFilepath"], ConfigurationManager.AppSettings["KeyFilePassword"]);
RSACryptoServiceProvider rsacsp = (RSACryptoServiceProvider)MSCert.PrivateKey;
CspParameters cspParam = new CspParameters();
cspParam.KeyContainerName = rsacsp.CspKeyContainerInfo.KeyContainerName;
cspParam.KeyNumber = rsacsp.CspKeyContainerInfo.KeyNumber == KeyNumber.Exchange ? 1 : 2;
RSACryptoServiceProvider aescsp = new RSACryptoServiceProvider(cspParam);
aescsp.PersistKeyInCsp = false;
byte[] signed = aescsp.SignData(requestBytes, "SHA256");

// For testing purposes - testing the signature
bool isValid = aescsp.VerifyData(requestBytes, "SHA256", signed);
string signatureValue = null;

// Deflate the signature string
using (var output = new MemoryStream())
{
    using (var zip = new DeflateStream(output, CompressionMode.Compress))
    {
        zip.Write(signed, 0, signed.Length);
    }
    var base64 = Convert.ToBase64String(output.ToArray());
    var urlEncode = HttpUtility.UrlEncode(base64);
    signatureValue = urlEncode;
}    

尽管如此，我看到验证失败了，有人能帮我看看原因吗