Untitled

<%@ Register TagPrefix="recaptcha" Namespace="Recaptcha" Assembly="Recaptcha" %>

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

<div class="g-recaptcha" data-sitekey="6LeIxAcTAAAAAJcZVRqyHh71UMIEGNQ_MXjiZKhI"></div>

<recaptcha:RecaptchaControl
    ID="recaptcha"
    runat="server"
    PublicKey="6LeIxAcTAAAAAJcZVRqyHh71UMIEGNQ_MXjiZKhI"
    PrivateKey="_My private key taken from the reCaptcha API_"
    />

<html>
    <head>
        <script src='https://www.google.com/recaptcha/api.js'></script>
    </head>
    <body>
        <form>

public partial class page : System.Web.UI.Page
{
    private string CAPTCHA_SECRET_KEY = @"6LeIxAcTAAAAAGG-vFI1TnRWxMZNFuojJ4WifJWe"; // WARNING: FAKE SECRET KEY
    protected void Page_Load(object sender, EventArgs e)
    {
        if(IsPostBack)
        {
            String username = unameInput.Text;
            String password = pwordInput.Text;

            if (validate())
            {
                // ...
            }
        }
    }

    // Thanks to http://www.thatsoftwaredude.com/content/6235/implementing-googles-no-captcha-recaptcha-in-aspnet
    private bool validate()
    {
        string url = @"https://www.google.com/recaptcha/api/siteverify";
        WebRequest request = WebRequest.Create(url);
        string postData = string.Format("secret={0}&response={1}&remoteip={2}", CAPTCHA_SECRET_KEY, Request["g-recaptcha-response"], Request.UserHostAddress);

        request.Method = "POST";
        request.ContentType = "application/x-www-form-urlencoded";
        request.ContentLength = postData.Length;

        StreamWriter writer = new StreamWriter(request.GetRequestStream());
        writer.Write(postData);
        writer.Close();

        StreamReader reader = new StreamReader(request.GetResponse().GetResponseStream());
        string responseData = reader.ReadToEnd();

        JavaScriptSerializer jss = new JavaScriptSerializer();
        CaptchaResponse cResponse = jss.Deserialize<CaptchaResponse>(responseData);
        return cResponse.success;
    }
    catch(WebException)
    {
        return true; // TODO: Change to false when releasing
    }
}
class CaptchaResponse
{
    public bool success { get; set; }
}