feat: implement mail-login directadmin plugin

exec/lib/RateLimiter.php

@@ -0,0 +1,38 @@
+<?php
+declare(strict_types=1);
+
+final class RateLimiter
+{
+    public function __construct(private string $dir)
+    {
+    }
+
+    public function assertAllowed(string $bucket, int $limit, int $windowSeconds): void
+    {
+        if ($limit < 1) {
+            throw new RuntimeException('Rate limit is invalid');
+        }
+        if (!is_dir($this->dir)) {
+            mkdir($this->dir, 0700, true);
+        }
+        $file = $this->dir . '/' . preg_replace('/[^A-Za-z0-9._-]/', '_', $bucket) . '.json';
+        $now = time();
+        $events = [];
+        if (is_file($file)) {
+            $decoded = json_decode((string)file_get_contents($file), true);
+            if (is_array($decoded)) {
+                foreach ($decoded as $event) {
+                    if (is_int($event) && $event > $now - $windowSeconds) {
+                        $events[] = $event;
+                    }
+                }
+            }
+        }
+        if (count($events) >= $limit) {
+            throw new RuntimeException('Rate limit exceeded');
+        }
+        $events[] = $now;
+        file_put_contents($file, json_encode($events), LOCK_EX);
+        @chmod($file, 0600);
+    }
+}