<% using (Html.BeginForm()) { %>
    <p>
        <%=Html.LabelFor(m => m.Username)%>
        <%=Html.TextBoxFor(m => m.Username)%>
    </p>
    <p>
        <%=Html.LabelFor(m => m.Password)%>
        <%=Html.TextBoxFor(m => m.Password)%>
    </p>
<%} %>
<script type="text/javascript">
    $("form").submit(function (evt) {
        // extract values to submit
        var form = $(this),
            username = form.find("[name=Username]").val(),
            password = form.find("[name=Password]").val(),
            json = JSON.stringify({
                Username: username,
                Password: password
            });

        $.ajax({
            url: form.attr("action"),
            type: 'POST',
            contentType: 'application/json; charset=utf-8',
            dataType: 'json',
            data: json,
            success: handleLogin
        });

        // stop form submitting
        evt.preventDefault();
    });
</script>