@if (Request.IsAuthenticated)
                {

                <li> @Html.ActionLink("Log Out", "LogOff", "User") </li>
                <li style="color:crimson">@Context.User.Identity.Name</li>
                }
                else
                {
                <li>@Html.ActionLink("Log On", "LogOn", "User")</li>
                <li>@Html.ActionLink("Register", "Register", "User")</li>}

<authentication mode="Forms">
  <forms loginUrl="~/User/LogOn" defaultUrl="~/Book/Index"/>
  </authentication>

[HttpPost]
    public ActionResult LogOn(LogOnModel model)
    {

        if (ModelState.IsValid)
        {

            if (Isvalid(model.Email, model.Pass)) {
               // FormsAuthentication.RedirectFromLoginPage(model.Email, false);
                FormsAuthentication.SetAuthCookie(model.Email, false);
                // Session["mail"] = model.Email;
                return RedirectToAction("Index", "Book");
             }
            else
            {
              ModelState.AddModelError("", "The user name or password provided is incorrect.");
            }

        }

        return View(model);
    }
    private bool Isvalid(string email, string password)
    {
        bool Isvalid = false;
        using (var db = new OperationDataContext())
        {
            var user = db.Users.FirstOrDefault(u => u.Email == email); //consultar el primer registro con los el email del usuario
            if (user != null)
            {
                if (user.Pass == password)  //Verificar password del usuario
                {
                    Isvalid = true;
                }
            }
        }
        return Isvalid;
    }

<authentication>

            <anonymousAuthentication enabled="true" userName="" />

            <basicAuthentication enabled="false" />

            <clientCertificateMappingAuthentication enabled="false" />

            <digestAuthentication enabled="false" />

            <iisClientCertificateMappingAuthentication enabled="false">
            </iisClientCertificateMappingAuthentication>

            <windowsAuthentication enabled="false">
                <providers>
                    <add value="Negotiate" />
                    <add value="NTLM" />
                </providers>
            </windowsAuthentication>

        </authentication>