MAPG-242 add possibility to captcha validation

.env.example

@@ -21,3 +21,5 @@ MULTI_INTERNAL_PORT=5000
 MULTI_WS_URL=mapguesser-dev.ch:8090
 MULTI_WS_PORT=8090
 ENABLE_GAME_FOR_GUESTS=0
+RECAPTCHA_SITEKEY=your_recaptcha_sitekey
+RECAPTCHA_SECRET=your_recaptcha_secret

src/Util/CaptchaValidator.php

@@ -0,0 +1,19 @@
+<?php namespace MapGuesser\Util;
+
+use MapGuesser\Http\Request;
+
+class CaptchaValidator
+{
+    public function validate(string $response)
+    {
+        $request = new Request('https://www.google.com/recaptcha/api/siteverify', Request::HTTP_GET);
+        $request->setQuery([
+            'secret' => $_ENV['RECAPTCHA_SECRET'],
+            'response' => $response
+        ]);
+
+        $response = $request->send();
+
+        return json_decode($response->getBody(), true);
+    }
+}