implement google captcha v2 in codeigniter 3

In your view file :

  <div id="captchav2"></div>

Create a div to display your captcha.

<input type="hidden" class="g-recaptcha-response" name="g-recaptcha-response">

Place it inside your form.

<script>
      var onloadCallback = function() {
        grecaptcha.render('captchav2', {
          'sitekey' : 'YOUR SITE KEY'
        });
      };
</script>

<script src="https://www.google.com/recaptcha/api.js?onload=onloadCallback&render=explicit"
        async defer>
</script>

Add towards the end of your view file.

In your controller function :

$captcha_response = trim($this->input->post('g-recaptcha-response'));

Add this inside your function.

if($captcha_response != ''): //true
          {
            $keySecret = 'YOUR SECRET KEY';

            $check = array(
              'secret'      =>  $keySecret,
              'response'    =>  $this->input->post('g-recaptcha-response')
            );

            $startProcess = curl_init();
            curl_setopt($startProcess, CURLOPT_URL, "https://www.google.com/recaptcha/api/siteverify");
            curl_setopt($startProcess, CURLOPT_POST, true);
            curl_setopt($startProcess, CURLOPT_POSTFIELDS, http_build_query($check));
            curl_setopt($startProcess, CURLOPT_SSL_VERIFYPEER, false);
            curl_setopt($startProcess, CURLOPT_RETURNTRANSFER, true);
            $receiveData = curl_exec($startProcess);
            $finalResponse = json_decode($receiveData, true);

              if($finalResponse['success'])
              {
                 //if success
              }
              else
              {
                 //if failed
              }    
           } 
else
{
   //if the user does not click the captcha v2
}