How to implement reCaptcha V3 in ASP.NET

Question

Does anyone have a full implementation demo of reCaptcha V3 in ASP.NET?

I found this article: Google Recaptcha v3 example demo

At the moment I am using reCap

Answer 1

Edit : I have added a demo project . Check this github repository . https://github.com/NIHAR-SARKAR/GoogleRecaptchav3-example-In-asp.net

From frontend (.aspx page) you need to send ajax request to pass the token to backend server . Using "recaptcha.execute" U can get the response , and pass the token using ajax request .Please check the code block .

 <script src="http://www.google.com/recaptcha/api.js?render=recaptchaSiteKey"></script>
<script>
 grecaptcha.ready(function() {
 grecaptcha.execute('recaptchaSiteKey', {action: 'homepage'}).then(function(token) {

            $.ajax({
                //pass the toket to Webmethod using Ajax
            });
          });
     });
</script>

Reference link: https://developers.google.com/recaptcha/docs/verify https://developers.google.com/recaptcha/docs/display#js_api

Now in the aspx.cs you need to write a "[WebMethod]" to receive the token from Ajax request .

    [WebMethod]
    public static void CaptchaVerify(string token)
    {
            var responseString = RecaptchaVerify(token);
            ResponseToken response = new ResponseToken();
            response = Newtonsoft.Json.JsonConvert.DeserializeObject<ResponseToken>(responseString.Result);

    }

To get the response from google recapcha api u need to use async call using httpClient . you also need to create a class which will contain same properties like the response string . After getting the "responseString" u need to convert the response to ResponseToken object by using Newtonsoft.Json. response = Newtonsoft.Json.JsonConvert.DeserializeObject<ResponseToken>(responseString.Result);

private string apiAddress = "https://www.google.com/recaptcha/api/siteverify";

private string recaptchaSecret = googleRecaptchaSecret;

        public async Task<string> RecaptchaVerify(string recaptchaToken)
        {
            string url = $"{apiAddress}?secret={recaptchaSecret}&response={recaptchaToken}";
            using (var httpClient = new HttpClient())
            {
                try
                {

                    string responseString=  httpClient.GetStringAsync(url).Result;
                    return responseString;

                }
                catch (Exception ex)
                {
                    throw new Exception(ex.Message);
                }
            }
        }


        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; }
        }

Answer 2

There are several Recaptcha libraries available for ASP.Net. I chose to use reCAPTCHA.AspNetCore because it provides an HtmlHelper.

Please note that this library only supports one ReCatpcha per page, and it doesn't support Recaptcha v3 passive monitoring on non-form pages.

Answer 3

The simplest:

a) in cshtml (at the top)

@section Scripts
{
    <script src="https://www.google.com/recaptcha/api.js?render=your site key"></script>
    <script>
        grecaptcha.ready(function () {
            grecaptcha.execute('your site key', { action: 'homepage' }).then(function (token) {
                document.getElementById("foo").value = token;
            });
        });
    </script>
}

b) in cshtml inside the form (just before /form>:

<input type="hidden" id="foo" name="foo" />

c) a function inside Pagemodel class:

public static bool ReCaptchaPassed(string gRecaptchaResponse)
{
    HttpClient httpClient = new HttpClient();
    
    var res = httpClient.GetAsync($"https://www.google.com/recaptcha/api/siteverify?secret=your secret key no quotes&response={gRecaptchaResponse}").Result;
    
    if (res.StatusCode != HttpStatusCode.OK)
        return false;

    string JSONres = res.Content.ReadAsStringAsync().Result;
    dynamic JSONdata = JObject.Parse(JSONres);
    
    if (JSONdata.success != "true")
        return false;

    return true;
}

Finally, inside OnPostAsync at the beginning:

if (!ModelState.IsValid) 
    return Page();
else
{
    if (!ReCaptchaPassed(Request.Form["foo"]))
    {
        ModelState.AddModelError(string.Empty, "You failed the CAPTCHA.");
        return Page();
    }
}