Async validation in UI extension (Windows Azure Pack)

ChangePassword.html

<!-- SYNOPSIS: Sample HTML snippet from an imaginary UI extension that makes use of async validation -->
<!-- NOTE: This UI snippet will send an ajax request to ChangePassword/ValidatePasswordStrength uri to validate the users' input -->
<div>
    <div id="changeMyPasswordForm">
        <div class="drawer-form-item">
            <label for="newPassword">New Password</label>
            <div>
                <input id="newPassword" name="newPassword" type="text" data-val="true"
                    data-val-length-min="6" data-val-length-max="64"
                    data-val-remote="enabled"
                    data-val-remote-url="ChangePassword/ValidatePasswordStrength" />
            </div>
        </div>
    </div>
</div>

ChangePasswordController.cs

// SYNOPSIS: This is a sample controller that pretends to change/validate user's password complexity
using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using System.Net;
using System.ServiceModel.Web;
using System.Web.Mvc;
using System.Web.UI;

namespace MyAzurePackExtension {

    [OutputCache(Location = OutputCacheLocation.None)]
    [JsonExceptionHandler]
    public class ChangePasswordController : Controller {
        /// <summary>
        /// POST: /ChangePassword/ValidatePasswordStrength
        /// </summary>
        [HttpPost]
        [ActionName("ValidatePasswordStrength")]
        [OutputCache(Location = OutputCacheLocation.None)]
        [AspNetCacheProfile("NoCache")]
        public JsonResult ValidatePasswordStrengthAsync(string newPassword)
        {
            // Just a very primitive validation to demonstrate the error case
            if (newPassword.StartsWith("password", StringComparison.OrdinalIgnoreCase)) {
                return Json("New password does not meet the complexity requirements, please try again.");
            }
            // Here we report back to the UI, pwd string has passed the validation criteria - show green mark to the user
            return Json(true);
        }
    }
}