@using (Html.BeginForm(new { ReturnUrl = ViewBag.ReturnUrl }))
{
<!-- some -->
}
@using (Html.BeginForm(new { ReturnUrl = ViewBag.ReturnUrl, @class = "myclass" }))
<form action="/Account/Login?ReturnUrl=%2F&class=myclass" method="post">
public ActionResult Login(string returnUrl)
{
ViewBag.ReturnUrl = returnUrl;
return View();
}