How to implement recaptcha 2.0 on ASP.NET? - asp.net

Question

I want to implement recaptcha 2.0 on my web page. I followed the steps from there by putting on client side:
<script src='https://www.google.com/recaptcha/api.js'></script>
and:
<div class="g-recaptcha" data-sitekey="my_data-sitekey"></div>
but, as far I understood, that's not enough. There is also something which must be done on server side. What and how should I do?

Answer 1

I made a simple and easy to use implementation.
Add the below class to your web project.
using System.Linq;
using System.Net.Http;
using Abp.Threading;
using Abp.Web.Models;
using Abp.Web.Mvc.Models;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Filters;
using Microsoft.AspNetCore.Mvc.ModelBinding;
using Microsoft.AspNetCore.Mvc.ViewFeatures;
using Newtonsoft.Json;
namespace WebDemo.Web.Attributes
{
public class ValidateRecaptchaAttribute : ActionFilterAttribute
{
private readonly string _propertyName;
private readonly string _secretKey;
private readonly string _errorViewName;
private readonly string _errorMessage;
private const string GoogleRecaptchaUrl = "https://www.google.com/recaptcha/api/siteverify?secret={0}&response={1}";
private const string SecretKey = "***YOUR PRIVATE KEY HERE***";
public ValidateRecaptchaAttribute(string propertyName = "RepatchaValue", string secretKey = SecretKey, string errorViewName = "Error", string errorMessage = "Invalid captcha!")
{
_propertyName = propertyName;
_secretKey = secretKey;
_errorViewName = errorViewName;
_errorMessage = errorMessage;
}
public override void OnActionExecuting(ActionExecutingContext context)
{
var model = context.ActionArguments.First().Value;
var propertyInfo = model.GetType().GetProperty(_propertyName);
if (propertyInfo != null)
{
var repatchaValue = propertyInfo.GetValue(model, null) as string;
var captchaValidationResult = ValidateRecaptcha(repatchaValue, _secretKey);
if (captchaValidationResult.Success)
{
base.OnActionExecuting(context);
return;
}
}
SetInvalidResult(context);
}
private void SetInvalidResult(ActionExecutingContext context)
{
var errorModel = new ErrorViewModel(new ErrorInfo(_errorMessage));
var viewResult = new ViewResult
{
ViewName = _errorViewName,
ViewData = new ViewDataDictionary(new EmptyModelMetadataProvider(), new ModelStateDictionary())
{
Model = errorModel
}
};
context.Result = viewResult;
}
private static RecaptchaResponse ValidateRecaptcha(string userEnteredCaptcha, string secretKey)
{
if (string.IsNullOrEmpty(userEnteredCaptcha))
{
return new RecaptchaResponse
{
Success = false,
ErrorCodes = new[] { "missing-input-response" }
};
}
using (var client = new HttpClient())
{
var result = AsyncHelper.RunSync<string>(() => client.GetStringAsync(string.Format((string)GoogleRecaptchaUrl, secretKey, userEnteredCaptcha)));
var captchaResponse = JsonConvert.DeserializeObject<RecaptchaResponse>(result);
return captchaResponse;
}
}
public class RecaptchaResponse
{
[JsonProperty("success")]
public bool Success { get; set; }
[JsonProperty("challenge_ts")]
public string ChallengeTs { get; set; } // timestamp of the challenge load (ISO format yyyy-MM-dd'T'HH:mm:ssZZ)
[JsonProperty("hostname")]
public string Hostname { get; set; } // the hostname of the site where the reCAPTCHA was solved
[JsonProperty("error-codes")]
public string[] ErrorCodes { get; set; } // optional
}
}
}
And usage is very simple;
[HttpGet]
[ValidateRecaptcha]
public ActionResult CreateProject(CreateModel model)
{
//your main code that needs to be done after captcha validation.
}

Answer 2

You have to get an api in order to use this google service.
https://developers.google.com/recaptcha/docs/start

Answer 3

Here is the vb.net code to validate captcha on server side
Public Function ValidateCaptcha() As Boolean
Dim valid As Boolean = False
Dim Ressponse As String = Request("g-recaptcha-response")
Dim strKey As String = ConfigurationManager.AppSettings("google.recaptcha.secretkey")
Dim req As HttpWebRequest = Net.WebRequest.Create("https://www.google.com/recaptcha/api/siteverify?secret=" + strKey + "&response=" + Ressponse)
Try
Using wResponse As WebResponse = req.GetResponse()
Using readStream As New StreamReader(wResponse.GetResponseStream())
Dim jsonResponse As String = readStream.ReadToEnd()
Dim js As New JavaScriptSerializer()
Dim data As MyObject = js.Deserialize(Of MyObject)(jsonResponse)
' Deserialize Json
valid = Convert.ToBoolean(data.success)
End Using
End Using
Return valid
Catch ex As Exception
Throw ex
End Try
End Function
here is the class MYObject
Public Class MyObject
Public Property success() As String
Get
Return m_success
End Get
Set(ByVal value As String)
m_success = Value
End Set
End Property
Private m_success As String
End Class
And you need to call this ValidateCaptcha() function from your button click event as below:
Protected Sub btnTrial_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnTrial.Click
If ValidateCaptcha() Then
'''''Do your query here'''''
End If
End Sub
Please refer How to Validate Recaptcha V2 Server side to get more details