To integrate a simple reCAPTCHA into my contact form i preffer to use my own code instead of some third party library.

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reCAPTCHA: Easy on Humans, Hard on Bots

Config

Create file in 'config/recaptcha.php'

return [
    'sitekey' => 'your-sitekey-here',
    'secretkey' => 'your-secretkey-here'
];

Class

Create file in 'app/Classes/Recaptcha.php'

<?php

namespace App\Classes;

class Recaptcha
{
    const SITE_VERIFY_URL = 'https://www.google.com/recaptcha/api/siteverify';

    public $secret;
    public $response;
    public $remoteip;

    public function verify() {
        $postfields = [
            'secret'   => $this->secret,
            'response' => $this->response,
            'remoteip' => ($this->remoteip == '::1' ? '127.0.0.1' : $this->remoteip)
        ];

        $ch = curl_init();

        curl_setopt($ch, CURLOPT_URL, self::SITE_VERIFY_URL);
        curl_setopt($ch, CURLOPT_POST, true);
        curl_setopt($ch, CURLOPT_POSTFIELDS, $postfields);
        curl_setopt($ch, CURLINFO_HEADER_OUT, false);
        curl_setopt($ch, CURLOPT_HEADER, false);
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
        curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, true);

        $response = curl_exec($ch);

        curl_close($ch);

        $oResponse = json_decode($response);

        return $oResponse->success;
    }
}

Add to autoloader in 'composer.json'

"autoload": {
    "files": [
        "app/Classes/Recaptcha.php"
    ]
}

Finnaly we need to regenerate ('vender\composer\autoload_classmap.php') the list of all classes that need to be included:

composer dump-autoload

View

Add script to template or view

<script src="//www.google.com/recaptcha/api.js"></script>

Add div -tag within <form> ... </form>

<div class="g-recaptcha" data-sitekey="{{ Config::get('recaptcha.sitekey') }}"></div>

Controller

use Config;
use App\Classes\Recaptcha;

Check if POST data is not empty

$aMessages = [
    'g-recaptcha-response.required' => trans('messages.required', ['name' => 'reCAPTCHA'])
];

$oValidator = Validator::make(Input::all(), [
    'g-recaptcha-response' => 'required'
], aMessages);

if ($oValidator->fails()) {
    $aErrors = $oValidator->errors();
}

Check if reCAPTCHA is valid

if ( ! count($aErrors)) {
    $oRecaptcha = new Recaptcha;

    $oRecaptcha->secret   = Config::get('recaptcha.secretkey');
    $oRecaptcha->response = Input::get('g-recaptcha-response');
    $oRecaptcha->remoteip = $request->getClientIp();

    if ( ! $oRecaptcha->verify()) {
        $aErrors['g-recaptcha-response'] = trans('messages.invalid', ['name' => 'reCAPTCHA']);
    }
}

Messages (optional)

Edit file 'resources\lang\en\messages.php':

return [
    'required' => ':name is required.',
    'invalid' => ':name is invalid.'
];