Adding a Google captcha "I'm not a robot"

I was helped by this article , everything is described in quite detail

If in short:

1. You need to get the API key and specify the domain of your site in the settings (localhost, if you want to test the captcha on the local language). There you are also provided with a piece of html that you need to copy to the form and the script file:

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

1. When you connect all this when sending the form to the server, the value will be passed along with the fields 'get-recaptcha-response'

Another point, if you do not use the serialize function, but manually collect the fields and send them by ajax, then you also need to get the get-racaptcha-response field manually, something like this:

_formData['g-recaptcha-response'] = grecaptcha.getResponse();

The function grecaptcha. GetResponse() is defined in the script that you enabled (point 1)

1. Now that you have sent the captcha code to the server, you need to process the request on the server. Connect the file with this code to your PHP handler forms:

    <?php
    /**
     * This is a PHP library that handles calling reCAPTCHA.
     *    - Documentation and latest version
     *          https://developers.google.com/recaptcha/docs/php
     *    - Get a reCAPTCHA API Key
     *          https://www.google.com/recaptcha/admin/create
     *    - Discussion group
     *          http://groups.google.com/group/recaptcha
     *
     * @copyright Copyright (c) 2014, Google Inc.
     * @link      http://www.google.com/recaptcha
     *
     * Permission is hereby granted, free of charge, to any person obtaining a copy
     * of this software and associated documentation files (the "Software"), to deal
     * in the Software without restriction, including without limitation the rights
     * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
     * copies of the Software, and to permit persons to whom the Software is
     * furnished to do so, subject to the following conditions:
     *
     * The above copyright notice and this permission notice shall be included in
     * all copies or substantial portions of the Software.
     *
     * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
     * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
     * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
     * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
     * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
     * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
     * THE SOFTWARE.
     */
    /**
     * A ReCaptchaResponse is returned from checkAnswer().
     */
    class ReCaptchaResponse
    {
        public $success;
        public $errorCodes;
    }
    class ReCaptcha
    {
        private static $_signupUrl = "https://www.google.com/recaptcha/admin";
        private static $_siteVerifyUrl =
            "https://www.google.com/recaptcha/api/siteverify?";
        private $_secret;
        private static $_version = "php_1.0";
        /**
         * Constructor.
         *
         * @param string $secret shared secret between site and ReCAPTCHA server.
         */
        function ReCaptcha($secret)
        {
            if ($secret == null || $secret == "") {
                die("To use reCAPTCHA you must get an API key from <a href='"
                    . self::$_signupUrl . "'>" . self::$_signupUrl . "</a>");
            }
            $this->_secret=$secret;
        }
        /**
         * Encodes the given data into a query string format.
         *
         * @param array $data array of string elements to be encoded.
         *
         * @return string - encoded request.
         */
        private function _encodeQS($data)
        {
            $req = "";
            foreach ($data as $key => $value) {
                $req .= $key . '=' . urlencode(stripslashes($value)) . '&';
            }
            // Cut the last '&'
            $req=substr($req, 0, strlen($req)-1);
            return $req;
        }
        /**
         * Submits an HTTP GET to a reCAPTCHA server.
         *
         * @param string $path url path to recaptcha server.
         * @param array  $data array of parameters to be sent.
         *
         * @return array response
         */
        private function _submitHTTPGet($path, $data)
        {
            $req = $this->_encodeQS($data);
            $response = file_get_contents($path . $req);
            return $response;
        }
        /**
         * Calls the reCAPTCHA siteverify API to verify whether the user passes
         * CAPTCHA test.
         *
         * @param string $remoteIp   IP address of end user.
         * @param string $response   response string from recaptcha verification.
         *
         * @return ReCaptchaResponse
         */
        public function verifyResponse($remoteIp, $response)
        {
            // Discard empty solution submissions
            if ($response == null || strlen($response) == 0) {
                $recaptchaResponse = new ReCaptchaResponse();
                $recaptchaResponse->success = false;
                $recaptchaResponse->errorCodes = 'missing-input';
                return $recaptchaResponse;
            }
            $getResponse = $this->_submitHttpGet(
                self::$_siteVerifyUrl,
                array (
                    'secret' => $this->_secret,
                    'remoteip' => $remoteIp,
                    'v' => self::$_version,
                    'response' => $response
                )
            );
            $answers = json_decode($getResponse, true);
            $recaptchaResponse = new ReCaptchaResponse();
            if (trim($answers ['success']) == true) {
                $recaptchaResponse->success = true;
            } else {
                $recaptchaResponse->success = false;
                $recaptchaResponse->errorCodes = $answers [error-codes];
            }
            return $recaptchaResponse;
        }
    }
    ?>

Next, you need to create a ReCapcha class in the handler and call the verifyResponse function:

// ваш секретный ключ
$secret = "6LcePAATAAAAABjXaTsy7gwcbnbaF5XgJKwjSNwT";
 
// пустой ответ
$response = null;
 
// проверка секретного ключа
$reCaptcha = new ReCaptcha($secret);

// if submitted check response
if ($_POST["g-recaptcha-response"]) {
    $response = $reCaptcha->verifyResponse(
        $_SERVER["REMOTE_ADDR"],
        $_POST["g-recaptcha-response"]
    );
}

if ($response != null && $response->success) {
    echo "Hi " . $_POST["name"] . " (" . $_POST["email"] . "), thanks for submitting the form!";
}