Use No Captcha reCaptcha In ASP.Net Web Application Form Page With C#, JSON and JavaScript

Users are getting more and more tired of interpreting images with random numbers or letters that take 2-3 tries to get. Google has a new release of the reCaptcha to include a  “No Captcha” feature. You can read about that more here. Here are the steps that I took to include this newer version into a ASP.Net web application.

• Obtain a google account and sign up for reCaptcha 
• Create a Visual Studio C# based web forms application and create a page where you will have your reCaptcha to live
• Download Json via NuGet (instructions are here)
• Once you have reCaptcha information be sure to insert the following in the head section of your web page:

 
<script src="https://www.google.com/recaptcha/api.js" type="text/javascript"></script> 

• Then place in your web page where you want the reCaptcha to live. Remember to replace “yoursitekey” with the Google reCaptcha site key:

<div class="g-recaptcha" data-sitekey="yoursitekey"></div>

• Create a class in your web application called ReCaptchaClass (credit for class and credit for proxy) and put the following code into the class. Remember to replace “yoursecretkeygoeshere” with the Google reCaptcha secret key:

using Newtonsoft.Json;
    public class ReCaptchaClass
    {
        public static string Validate(string EncodedResponse)
        {
            var client = new System.Net.WebClient();
            IWebProxy defaultWebProxy = WebRequest.DefaultWebProxy;
            defaultWebProxy.Credentials = CredentialCache.DefaultCredentials;
            client.Proxy = defaultWebProxy;
            string PrivateKey = "yoursecretkeygoeshere";
            var GoogleReply = client.DownloadString(string.Format("https://www.google.com/recaptcha/api/siteverify?secret={0}&response={1}", PrivateKey, EncodedResponse));
            var captchaResponse = Newtonsoft.Json.JsonConvert.DeserializeObject(GoogleReply);
            return captchaResponse.Success;
        }
        [JsonProperty("success")]
        public string Success
        {
            get { return m_Success; }
            set { m_Success = value; }
        }

        private string m_Success;
        [JsonProperty("error-codes")]
        public List ErrorCodes
        {
            get { return m_ErrorCodes; }
            set { m_ErrorCodes = value; }
        }
        private List m_ErrorCodes;
    }

• Once the class is created place the following snippet in the code behind of your page (likely in a button click event of some kind):

string EncodedResponse = Request.Form["g-Recaptcha-Response"];
bool IsCaptchaValid = (ReCaptchaClass.Validate(EncodedResponse) == "True" ? true : false);

if (IsCaptchaValid) {
    //Valid Request
}

That’s it! Easy enough, right? I hope it helps. Questions are always welcome.