M8: Security-Headers, Rate-Limits und Audit-Log

Erste drei Bausteine der Haertung:

- Security-Headers (X-Content-Type-Options, X-Frame-Options, Referrer-
  Policy, Permissions-Policy, HSTS bei HTTPS) laufen automatisch ueber
  app_send_security_headers() am Ende von app/bootstrap.php fuer jede
  dynamische Seite; landing.php war als einzige Seite ganz ohne PHP und
  bekam einen minimalen Bootstrap-Aufruf. Bewusst kein CSP, da die
  bestehenden Templates durchgaengig auf Inline-style-Attribute setzen.
- DB-gestuetzte Rate-Limits (neue Tabelle rate_limit_attempts) fuer
  Login (10/15min je E-Mail, 20/15min je IP), Registrierung (5/h je IP)
  und Passwort-Reset-Anfrage (5/h je E-Mail, 10/h je IP); bei
  ausgereiztem Reset-Limit erscheint dieselbe generische Meldung wie im
  Erfolgsfall, um kein Konto-Enumeration-Signal zu geben.
- Zentrales Audit-Log (neue Tabelle audit_log) fuer Mitgliederverwaltung,
  Zugangsvergabe/-entzug, Storno, Mandant-Einstellungen, Hinweise,
  CSV-Import, Jahresbonus-Verteilung und Live-Mailversand; sichtbar fuer
  Owner/Admin auf mandant-einstellungen.php.

Live getestet: Rate-Limit greift nach 10 Fehlversuchen, Audit-Log-Eintrag
mit korrekten Metadaten und Nutzernamen ueber einen isolierten Test-
Mandanten geprueft. Alle Regressionstests weiterhin gruen (26/26 Smoke,
104 Golden-Master-Assertions).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/audit.php

@@ -0,0 +1,53 @@
+<?php
+
+declare(strict_types=1);
+
+require_once __DIR__ . '/bootstrap.php';
+
+/**
+ * Records one admin/security-relevant action. Keep $action as a short,
+ * stable slug (e.g. "participant.access_granted") so entries stay
+ * filterable; put anything variable in $metadata.
+ */
+function app_audit_log(
+    PDO $pdo,
+    ?int $tenantId,
+    ?int $actorUserId,
+    string $action,
+    string $subjectType,
+    ?int $subjectId,
+    array $metadata = []
+): void {
+    $stmt = $pdo->prepare(
+        'INSERT INTO audit_log (tenant_id, actor_user_id, action, subject_type, subject_id, metadata_json, ip)
+         VALUES (?, ?, ?, ?, ?, ?, ?)'
+    );
+    $stmt->execute([
+        $tenantId,
+        $actorUserId,
+        $action,
+        $subjectType,
+        $subjectId,
+        $metadata !== [] ? json_encode($metadata, JSON_UNESCAPED_UNICODE) : null,
+        $_SERVER['REMOTE_ADDR'] ?? null,
+    ]);
+}
+
+/**
+ * @return list<array{id: int, actor_user_id: ?int, actor_name: ?string, action: string, subject_type: string, subject_id: ?int, metadata_json: ?string, ip: ?string, created_at: string}>
+ */
+function app_fetch_audit_log(PDO $pdo, int $tenantId, int $limit = 100): array
+{
+    $limit = max(1, min($limit, 500));
+    $stmt = $pdo->prepare(
+        "SELECT a.id, a.actor_user_id, u.display_name AS actor_name, a.action, a.subject_type, a.subject_id, a.metadata_json, a.ip, a.created_at
+         FROM audit_log a
+         LEFT JOIN users u ON u.id = a.actor_user_id
+         WHERE a.tenant_id = ?
+         ORDER BY a.created_at DESC, a.id DESC
+         LIMIT {$limit}"
+    );
+    $stmt->execute([$tenantId]);
+
+    return $stmt->fetchAll();
+}

app/bootstrap.php

@@ -27,6 +27,29 @@ function app_is_https(): bool
         || (($_SERVER['SERVER_PORT'] ?? null) === '443');
 }
 
+/**
+ * Sends baseline security headers on every dynamic request. Deliberately
+ * does not set a Content-Security-Policy: the existing templates rely on
+ * inline style="" attributes throughout (banners, table cells, etc.), and
+ * locking that down would need a broader template pass. Runs once per
+ * request via the auto-invocation at the bottom of this file.
+ */
+function app_send_security_headers(): void
+{
+    if (PHP_SAPI === 'cli' || headers_sent()) {
+        return;
+    }
+
+    header('X-Content-Type-Options: nosniff');
+    header('X-Frame-Options: DENY');
+    header('Referrer-Policy: strict-origin-when-cross-origin');
+    header('Permissions-Policy: geolocation=(), microphone=(), camera=()');
+
+    if (app_is_https()) {
+        header('Strict-Transport-Security: max-age=31536000; includeSubDomains');
+    }
+}
+
 function app_start_session(): void
 {
     if (PHP_SAPI === 'cli' || session_status() === PHP_SESSION_ACTIVE) {
@@ -102,3 +125,5 @@ function app_require_csrf(): void
         die('CSRF validation failed.');
     }
 }
+
+app_send_security_headers();

app/rate-limit.php

@@ -0,0 +1,34 @@
+<?php
+
+declare(strict_types=1);
+
+require_once __DIR__ . '/bootstrap.php';
+
+function app_client_ip(): string
+{
+    return (string)($_SERVER['REMOTE_ADDR'] ?? 'unknown');
+}
+
+/**
+ * Records an attempt in the given bucket and reports whether the caller is
+ * still within the allowed rate. Call before doing the sensitive work (auth
+ * check, mail dispatch, account creation); if this returns false, show a
+ * generic "too many attempts" message without processing the request, so a
+ * bucket also can't be used to enumerate valid accounts by timing.
+ */
+function app_rate_limit_check(PDO $pdo, string $bucket, int $maxAttempts, int $windowSeconds): bool
+{
+    $pdo->prepare('INSERT INTO rate_limit_attempts (bucket) VALUES (?)')->execute([$bucket]);
+
+    // Opportunistic cleanup so the table doesn't grow unbounded; scoped to
+    // this bucket to keep each call cheap.
+    $pdo->prepare('DELETE FROM rate_limit_attempts WHERE bucket = ? AND created_at < DATE_SUB(NOW(), INTERVAL ? SECOND)')
+        ->execute([$bucket, $windowSeconds]);
+
+    $stmt = $pdo->prepare(
+        'SELECT COUNT(*) FROM rate_limit_attempts WHERE bucket = ? AND created_at >= DATE_SUB(NOW(), INTERVAL ? SECOND)'
+    );
+    $stmt->execute([$bucket, $windowSeconds]);
+
+    return (int)$stmt->fetchColumn() <= $maxAttempts;
+}