How to implement Captcha v3 in ASP.NET

 I was facing an issue of dom parsing in my website. I finally resolved it by using Google Captcha V3.

Step 1: Get your keys from
https://developers.google.com/recaptcha/intro

Step 2: Use the below example code:

.ASPX

<%@ Page Title="Home Page" Language="C#" MasterPageFile="~/Site.Master" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="Captchav3._Default" %>

<asp:Content runat="server" ID="FeaturedContent" ContentPlaceHolderID="FeaturedContent">
    <section class="featured">
        <div class="content-wrapper">
        </div>
    </section>
</asp:Content>
<asp:Content runat="server" ID="BodyContent" ContentPlaceHolderID="MainContent">
        <h3>Login Form</h3>
        <asp:HiddenField ID="LoginId" runat="server" />
        Login:<asp:TextBox ID="txtLogin" runat="server"></asp:TextBox><br />
        Password:<asp:TextBox ID="txtPassword" runat="server"></asp:TextBox><br />
        <asp:Button ID="btnLogin" runat="server" Text="Login" OnClick="btnLogin_Click" />
        <script src="https://www.google.com/recaptcha/api.js?render=6Lc7ctQUXXXXXzgKdup36qsMS-y_Hc6JCwAn_Bd"></script>
        <script>
            grecaptcha.ready(function () {
                grecaptcha.execute('6Lc7ctQUXXXXXzgKdup36qsMS-y_Hc6JCwAn_Bd', { action: 'umslogin' }).then(function (token) {
                    document.getElementById('<%= LoginId.ClientID%>').value = token;
            });
        });
        </script>
</asp:Content>



C#

 public partial class _Default : Page
    {
        private static string Token = string.Empty;
        protected void Page_Load(object sender, EventArgs e)
        {
            Token = LoginId.Value;
        }
        private static ResponseToken response = new ResponseToken();
      
        private string CaptchaVerify()
        {
            if (response.score == 0)
            {
                var responseString = RecaptchaVerify(Token);
                response = JsonConvert.DeserializeObject<ResponseToken>(responseString.Result);

            }
            return JsonConvert.SerializeObject(response);
            //return "";
        }
        private static string apiAddress = "https://www.google.com/recaptcha/api/siteverify";
        private static async Task<string> RecaptchaVerify(string recaptchaToken)
        {
            string url = apiAddress + "?secret=6Lc7ctQUXXXXXL--lngI_gIyRFyToplpKvZmMVlj&response=" + recaptchaToken;
            using (HttpClient httpClient = new HttpClient())
            {
                try
                {
                    string responseString = httpClient.GetStringAsync(url).Result;
                    return responseString;
                    //dynamic json = JsonConvert.DeserializeObject(responseString);
                    //return json.success;
                }
                catch (Exception ex)
                {
                    throw new Exception(ex.Message);
                }
            }
        }

        protected void btnLogin_Click(object sender, EventArgs e)
        {
            dynamic o = JsonConvert.DeserializeObject(CaptchaVerify());
            if (o.Success.Value)
            {
                if (o.score.Value > 0.3)
                {
                    Response.Write("<h1>Valid Request</h1>");
                    if (txtLogin.Text == "admin" && txtPassword.Text == "admin")
                    {
                        Response.Write("Logged In Successfully");
                    }
                }
                else
                {
                    Response.Write("<h1>Not a Valid Request</h1>");
                    Response.StatusCode = 403;
                }
            }
            else
            {
                Response.Write("<h1>Not a Valid Request</h1>");
                Response.StatusCode = 403;
            }

        }
    }
    public class ResponseToken
    {

        public DateTime challenge_ts { get; set; }
        public float score { get; set; }
        public List<string> ErrorCodes { get; set; }
        public bool Success { get; set; }
        public string hostname { get; set; }
    }