public class BaseController : Controller
{
    public JsonResult CreateResponse(object data, bool allowGet)
    {
        return Json(data, allowGet);
    }
    public JsonResult CreateResponse(object data)
    {
        return Json(data, JsonRequestBehavior.AllowGet);
    }
}

public class HomeController : BaseController
{
    [HttpGet]
    public JsonResult Login(LoginUserModel model)
    {
        using (JeritEntities db = new JeritEntities())
        {
            try
            {
                if (DoLogin(model.EmailAddress, model.Password)
                {
                    return CreateResponse(true)
                }
                return CreateResponse(Json(new { IsOk = false, Title = "Log In", Message = "Invalid user credentials" }));
            }
            catch (Exception ex)
            {
                // just report the error
                return CreateResponse(Json(new { IsOk = false, Title = "Log In", Message = ex.Message }));
            }
        }
    }
}

// here follows the view ~/Index.cshtml

<main class="mdl-layout__content">
    <div class="page-content">
        @RenderBody()

        <dialog class="mdl-dialog">
            <h4 class="mdl-dialog__title"></h4>
            <div class="mdl-dialog__content">
                <p></p>
            </div>
            <div class="mdl-dialog__actions">
                <button type="button" class="mdl-button ok">OK</button>
                <button type="button" class="mdl-button close">Close</button>
            </div>
        </dialog>
    </div>
</main>
<script>
    $("a.login").on("click", function () {
        Login();
    });

    function Login() {
        $("#p2").show(); // indicate work in progress
        var EmailAddress = $("#EmailAddress").val();
        var Password = $("#Password").val();

        console.log("Email Address " + EmailAddress);
        console.log("Password " + Password);

        var User = {
            "EmailAddress": EmailAddress, "Password": Password
        };
        $.post("/Home/Login", User, function (data) {
            if (!data) {
                $("#p2").hide();
                console.log("Title: " + data.Title); // value undefined
                console.log("Message: " + data.Message); // value undefined
                showMessage(data.Title, data.Message);
            }
            else
            {
                window.location.href = '@Url.Content("~/")';
            }
        });
    }

    function showMessage(title, msg) {
        var dialog = document.querySelector('dialog');
        if (!dialog.showModal) {
            dialogPolyfill.registerDialog(dialog);
        }
        $(".mdl-dialog__title").html(title);
        $(".mdl-dialog__content p").html(msg);
        dialog.querySelector('.ok').addEventListener('click', function () {
            dialog.close();
        });
        dialog.querySelector('.close').addEventListener('click', function () {
            dialog.close();
        });
        $("button.close").hide();

        dialog.showModal();
    }
</script>