harden(rate-limiter): fail secure login scopes with cache fallback

core/Service/Security/RateLimiterFallbackGateway.php

@@ -0,0 +1,35 @@
+<?php
+
+namespace MintyPHP\Service\Security;
+
+use MintyPHP\Cache;
+
+class RateLimiterFallbackGateway
+{
+    private const KEY_PREFIX = 'rate_limit_fallback:';
+
+    public function load(string $scope, string $subjectHash): ?array
+    {
+        $state = Cache::get($this->key($scope, $subjectHash));
+        if (!is_array($state)) {
+            return null;
+        }
+
+        return $state;
+    }
+
+    public function save(string $scope, string $subjectHash, array $state, int $ttlSeconds): bool
+    {
+        return Cache::set($this->key($scope, $subjectHash), $state, max(1, $ttlSeconds));
+    }
+
+    public function remove(string $scope, string $subjectHash): void
+    {
+        Cache::delete($this->key($scope, $subjectHash));
+    }
+
+    private function key(string $scope, string $subjectHash): string
+    {
+        return self::KEY_PREFIX . strtolower(trim($scope)) . ':' . trim($subjectHash);
+    }
+}