include antiforgerytoken in ajax post ASP.NET MVC

You have incorrectly specified the contentType to application/json.

Here’s an example of how this might work.

Controller:

public class HomeController : Controller
{
    public ActionResult Index()
    {
        return View();
    }

    [HttpPost]
    [ValidateAntiForgeryToken]
    public ActionResult Index(string someValue)
    {
        return Json(new { someValue = someValue });
    }
}

View:

@using (Html.BeginForm(null, null, FormMethod.Post, new { id = "__AjaxAntiForgeryForm" }))
{
    @Html.AntiForgeryToken()
}

<div id="myDiv" data-url="@Url.Action("Index", "Home")">
    Click me to send an AJAX request to a controller action
    decorated with the [ValidateAntiForgeryToken] attribute
</div>

<script type="text/javascript">
    $('#myDiv').submit(function () {
        var form = $('#__AjaxAntiForgeryForm');
        var token = $('input[name="__RequestVerificationToken"]', form).val();
        $.ajax({
            url: $(this).data('url'),
            type: 'POST',
            data: { 
                __RequestVerificationToken: token, 
                someValue: 'some value' 
            },
            success: function (result) {
                alert(result.someValue);
            }
        });
        return false;
    });
</script>