MVC2和会话

我在使用验证码发生器。 http://xcaptcha.codeplex.com/ Session.Add 用于比较验证码生成与应答。我想让这成为我的模型的规则违反检查的一部分,但我似乎找不到/与会话的正确部分有工作。我是否错过了从模型的GetRuleViolations中导航到会话的方法?还有其他建议吗

// Controller
public ActionResult Image()
{
    var builder = new XCaptcha.ImageBuilder();
    var result = builder.Create();
    Session.Add("CaptchaKey", result.Solution);
    return new FileContentResult(result.Image, result.ContentType);
}

// My model
public IEnumerable<RuleViolation> GetRuleViolations()
{
    // This isn't correct... it isn't stored in server variables
    string captchaAnswer = HttpContext.Current.Request.ServerVariables.Get("CaptchaKey");
    // No such thing..
    string res = Session["Something"].ToString();
}

// My eh solution
// Controller
[HttpPost]
public ActionResult ContactUs(EmailModel e, FormCollection collection)
{
    string captchaAnswer = Session["CaptchaKey"].ToString();
    string captchaText = collection["CaptchaText"].ToUpper().ToString();
    bool correctCaptcha = (captchaAnswer.CompareTo(captchaText) == 0) ? true : false;

    if (e.IsValid && correctCaptcha)
    {
        EmailHelper.SendMessage(e);
        return RedirectToAction("ContactSuccess");
    }
    else
    {
        if (!correctCaptcha)
            ModelState.AddModelError("Captcha", "Incorrect Captcha answer");

        ModelState.AddRuleViolations(e.GetRuleViolations());
    }

    return View(e);
}