Validate Google reCaptcha with PHP.

util_helpers.php

/**
 * Validate Google reCAPTCHA
 *
 * @link   https://developers.google.com/recaptcha/docs/v3
 * @author Andrei Andrade
 *
 * @param mixed      $publicKey  The shared key between your site and reCAPTCHA.
 * @param mixed      $privateKey The user response token provided by the reCAPTCHA client-side integration on your site.
 * @param float      $score      Score value (1.0 is very likely a good interaction, 0.0 is very likely a bot).
 * @param null|mixed $remoteIp   Optional. The user's IP address.
 *
 * @return bool
 */
function isGoogleReCaptchaValid($publicKey, $privateKey, $score = 0.5, $remoteIp = null)
{
    $post = [
        'secret'   => $privateKey,
        'response' => $publicKey,
        'remoteip' => $remoteIp,
    ];

    $ch = curl_init('https://www.google.com/recaptcha/api/siteverify');
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($ch, CURLOPT_POSTFIELDS, $post);

    $response = curl_exec($ch);
    $response = json_decode($response);

    curl_close($ch);

    if ($response->success && $response->score >= $score) {
        return true;
    } else {
        return false;
    }
}