当SQL Server以域帐户而不是SYSTEM或NETWORK SERVICE的身份运行时，SQL CLR功能无法模拟

      currentIdentity = SqlContext.WindowsIdentity;
      impersonatedIdentity = currentIdentity.Impersonate();

       client.PreAuthenticate = true;
       client.Credentials = CredentialCache.DefaultNetworkCredentials;
       client.Url = currentURL;

   /* Encrypt */
   try
   {
      encryptedText = client.Encrypt(plainText);
   }
   finally
    {
        if (impersonatedIdentity != null)
        {
            impersonatedIdentity.Undo();
        }
    }

        return encryptedText;