Add Google reCAPTCHA v2 to ASP.Net Website

The official document to add google reCAPTCHA v2 to the asp.net website is here:  

https://developers.google.com/recaptcha/docs/display

A good article to follow is here:

https://www.c-sharpcorner.com/article/integration-of-google-recaptcha-in-w

After registering the  reCAPTCHA keys from here:

https://www.google.com/recaptcha/admin

Step 1- Add following code to the aspx file to show the reCAPTCHA control:

        <div class="form-item" id="divRecaptcha" runat="server">

                <div class="slickbutton clearfix" style="margin:5px auto;width:100%;text-align:center;">

                    <div data-theme="light" class="g-recaptcha" data-sitekey="sample public key"></div>

                </div>

           </div>

           <script src="https://www.google.com/recaptcha/api.js" async defer></script>

Step 2 - Add  following code to the C# code behand the page:

    public bool IsReCaptchaValid()

    {

        var result = false;

        var captchaResponse = Request.Form["g-recaptcha-response"];

        var secretKey = "Private Key";

        var apiUrl = "https://www.google.com/recaptcha/api/siteverify?secret={0}&response={1}";

        var requestUri = string.Format(apiUrl, secretKey, captchaResponse);

        var request = (HttpWebRequest)WebRequest.Create(requestUri);

        using (WebResponse response = request.GetResponse())

        {

            using (StreamReader stream = new StreamReader(response.GetResponseStream()))

            {

                JObject jResponse = JObject.Parse(stream.ReadToEnd());

                var isSuccess = jResponse.Value<bool>("success");

                result = (isSuccess) ? true : false;

            }

        }

        return result;

    }

Step 2 - Call the ReCaptcha check function in the Submit event code. If recaptcha not valid, show a warning message on the page:

   bool bIsRobot = IsReCaptchaValid();

        if (bIsRobot == false)

        {

            string strErrorMessage = "<ul>";

            strErrorMessage += "<li>Please check reCAPTCHA.</li>";

            strErrorMessage += "</ul>";

            divcontacte.InnerHtml = strErrorMessage;

            divcontacte.Visible = true;

            return;

        }

        else {

            divRecaptcha.Visible = false;

        }

Final note: it is possible to use Google reCAPTCHA in countries where Google is not accessible. Just use "www.recaptcha.net"   instead of "www.google.com" as mentioned in  following article:

 https://developers.google.com/recaptcha/docs/faq#:~: