Add JSON endpoint for CAPTCHA rendering

To be used inside WP/WC registration form to construct URL for CAPTCHA page.

[MAILPOET-6325]

mailpoet/lib/API/JSON/v1/Captcha.php

@@ -0,0 +1,33 @@
+<?php declare(strict_types = 1);
+
+namespace MailPoet\API\JSON\v1;
+
+use MailPoet\API\JSON\Endpoint as APIEndpoint;
+use MailPoet\Captcha\CaptchaSession;
+use MailPoet\Captcha\CaptchaUrlFactory;
+use MailPoet\Config\AccessControl;
+
+class Captcha extends APIEndpoint {
+  private CaptchaSession $captchaSession;
+  private CaptchaUrlFactory $urlFactory;
+
+  public $permissions = [
+    'global' => AccessControl::NO_ACCESS_RESTRICTION,
+  ];
+
+  public function __construct(
+    CaptchaSession $captchaSession,
+    CaptchaUrlFactory $urlFactory
+  ) {
+    $this->captchaSession = $captchaSession;
+    $this->urlFactory = $urlFactory;
+  }
+
+  public function render(array $data = []) {
+    $sessionId = $this->captchaSession->generateSessionId();
+    $data = array_merge($data, ['captcha_session_id' => $sessionId]);
+    $captchaUrl = $this->urlFactory->getCaptchaUrl($data);
+
+    return $this->redirectResponse($captchaUrl);
+  }
+}