ip_json.php

<?php

switch ($_SERVER["REQUEST_METHOD"]) {
    case "GET":
        header("Access-Control-Allow-Origin: *");
        header("Content-Type: application/json; charset=utf-8");
        header("Cache-Control: no-store");
        $remote_addr = $_SERVER["REMOTE_ADDR"];
        $remote_host = $_SERVER["REMOTE_HOST"];
        if ($remote_host === $remote_addr) {
            $remote_host = gethostbyaddr($remote_addr);
        }
        print(json_encode(
            [
                "ip"       => $remote_addr,
                "hostname" => $remote_host
            ]
        ));
        break;
    case "OPTIONS":
        header("Access-Control-Allow-Origin: *");
        header("Access-Control-Max-Age: 0");
        header("Access-Control-Allow-Methods: GET, OPTIONS");
        header("Access-Control-Allow-Headers: Content-Type");
        http_response_code(204);
        break;
    default:
        http_response_code(405);
        break;
}