获取用于用户注册的源站/参照者的URL

我有一段代码,我测试了一个简单的用户注册码:

   ReferrerURL = Request.UrlReferrer.AbsoluteUri

例如,如果用户通过某个广告点击了这个站点,我想得到他来自的源站点。

通过这段代码,我只得到了我自己网站的URL,它看起来像:

example.com/Registration

[ValidateAntiForgeryToken]
public async Task<ActionResult> DoRegister(UserRegistrationViewModel model)
{
    var user = new Users()
    {
       FirstName = model.FirstName,
       LastName = model.LastName,
       Email = model.Email,
       CountryId = 230,
       Active = false,
       PasswordSalt = salt,
       PasswordHash = PasswordHelper.CreatePasswordHash(model.Password, salt),
       GUID = _guid,
       HasSpecialSubscription = false,
       TotalScans = 0,
       IsFreeTrialExpired = false,
       DateOfRegistration = DateTime.Now,
       ReferrerId = referrerId,
       AffiliatePct = 0.15,
       Cycles = 3,
       ReferrerURL = Request.UrlReferrer.AbsoluteUri
    };
}