[ticket/17414] Add get_hidden_fields to interface

PHPBB-17414

phpBB/phpbb/captcha/plugins/plugin_interface.php

@@ -52,6 +52,13 @@ interface plugin_interface
 	 */
 	public function init(int $type): void;
 
+	/**
+	 * Get hidden form fields for this captcha plugin
+	 *
+	 * @return array Hidden form fields
+	 */
+	public function get_hidden_fields(): array;
+
 	/**
 	 * Validate the captcha with the given request data
 	 *