feat(guild-events): add HMAC-signed webhook delivery and replay guards

Fabric.Backend.Guild/src/events/events.service.ts

@@ -1,10 +1,25 @@
 import { Injectable, Logger } from '@nestjs/common';
-import { randomUUID } from 'crypto';
+import { createHmac, randomUUID } from 'crypto';
 import { FabricEventEnvelope } from './event-envelope';
 
 @Injectable()
 export class EventsService {
   private readonly logger = new Logger(EventsService.name);
+  private readonly sentEventIds = new Map<string, number>();
+
+  private cleanupSentCache(now: number): void {
+    const ttlMs = 10 * 60 * 1000;
+    for (const [eventId, ts] of this.sentEventIds.entries()) {
+      if (now - ts > ttlMs) this.sentEventIds.delete(eventId);
+    }
+  }
+
+  private signWebhook(payload: string, timestamp: string, nonce: string): string {
+    const secret = process.env.FABRIC_WEBHOOK_SECRET;
+    if (!secret) return '';
+    const canonical = ['POST', '/webhook/events', timestamp, nonce, payload].join('\n');
+    return createHmac('sha256', secret).update(canonical).digest('hex');
+  }
 
   buildEnvelope(input: {
     eventType: string;
@@ -32,21 +47,39 @@ export class EventsService {
     data: Record<string, unknown>;
   }): Promise<FabricEventEnvelope> {
     const envelope = this.buildEnvelope(input);
+    const now = Date.now();
+    this.cleanupSentCache(now);
+
+    if (this.sentEventIds.has(envelope.event_id)) {
+      this.logger.warn(`skip duplicate event_id: ${envelope.event_id}`);
+      return envelope;
+    }
 
     const webhookUrl = process.env.FABRIC_WEBHOOK_URL;
     if (!webhookUrl) {
       this.logger.log(`event(no-webhook): ${JSON.stringify(envelope)}`);
+      this.sentEventIds.set(envelope.event_id, now);
       return envelope;
     }
 
     try {
+      const timestamp = new Date(now).toISOString();
+      const nonce = randomUUID();
+      const payload = JSON.stringify(envelope);
+      const signature = this.signWebhook(payload, timestamp, nonce);
+
       await fetch(webhookUrl, {
         method: 'POST',
         headers: {
           'content-type': 'application/json',
+          'x-fabric-version': '1',
+          'x-fabric-timestamp': timestamp,
+          'x-fabric-nonce': nonce,
+          'x-fabric-signature': signature,
         },
-        body: JSON.stringify(envelope),
+        body: payload,
       });
+      this.sentEventIds.set(envelope.event_id, now);
     } catch (error) {
       const message = error instanceof Error ? error.message : String(error);
       this.logger.warn(`event delivery failed: ${message}`);