Google new reCAPTCHA using asp.net mvc

Just follow the following steps in order implement Google new reCAPTCHA using asp.net MVC 

Step-1: Create New Project.

Go to File > New > Project > ASP.NET  Web Application (under web) > Entry Application Name > Click OK > Select Basic > Select view engine Razor > OK

Step-2: Sign up & Generate Google reCAPTCHA API

Go to http://www.google.com/recaptcha then click on the top right corner Get reCAPTCHA button. Here you will get a form for Register a new site, fill the form and complete your registration. After complete your registration you will get Site key and Secret key those we will use in our application.

Step-3: Create a Controller.

Go to Solution Explorer > Right Click on Controllers folder form Solution Explorer > Add > Controller > Enter Controller name > Select Templete "empty MVC Controller"> Add.

Here I have created a controller "HomeController"

Step-4: Add new action into the controller to get the view, where we will implement Google reCAPTCHA

Here I have added "Index" Action into "Home" Controller. Please write this following code

public ActionResult Index()
{
    return View();
}

Step-5: Add view for the action (here "Index") & design.

Right Click on Action Method (here right click on Index action) > Add View... > Enter View Name > Select View Engine (Razor) > Add.

Complete HTML code 

@{
    ViewBag.Title = "Index";
}
<h2>Index</h2>
<div>
    @using (Html.BeginForm("FormSubmit", "Home", FormMethod.Post))
{
    <div class="g-recaptcha" data-sitekey="Your sitekey here"></div>
    <input type="submit" value="Submit" />
}
</div>
<span style="display:inline-block; font-size:20px;margin:20px 0;padding:20px;border:1px solid #D3D3D3">
    @ViewBag.Message
</span>
<script src='https://www.google.com/recaptcha/api.js' type="text/javascript"></script>

Step-6: Add reference of Newtonsoft.Json (if not already added in your project)

Here I have added Newtonsoft.Json reference from NuGet packages

Go to Solution Explorer > Right click on References > Manage NuGet packages > Search with "System.Linq.Dynamic" > Install.

Step-7: Add another action (here "FormSubmit") for form submit, where we will check google reCAPTCHA validity

[HttpPost]
public ActionResult FormSubmit()
{
    //Validate Google recaptcha here
    var response = Request["g-recaptcha-response"];
    string secretKey = "Your secret here";
    var client = new WebClient();
    var result = client.DownloadString(string.Format("https://www.google.com/recaptcha/api/siteverify?secret={0}&response={1}", secretKey, response));
    var obj = JObject.Parse(result);
    var status = (bool)obj.SelectToken("success");
    ViewBag.Message = status ? "Google reCaptcha validation success" : "Google reCaptcha validation failed";
 
    //When you will post form for save data, you should check both the model validation and google recaptcha validation
    //EX.
    /* if (ModelState.IsValid && status)
    {
 
    }*/
 
    //Here I am returning to Index page for demo perpose, you can use your view here
    return View("Index");
}

Step-8: Run Application (before run, make sure you have added your site key & secret key)