feat(webhook): implement Phase 1 webhook receiver for Sonarr and Radarr

- Added POST /api/webhook/sonarr and POST /api/webhook/radarr endpoints
- Implemented webhook secret validation via SOFARR_WEBHOOK_SECRET environment variable
- Added logging for all incoming webhook events using existing logToFile utility
- Returns HTTP 200 immediately to prevent webhook retries
- Mounted webhook routes before CSRF middleware (called by external services)
- Non-breaking: no changes to polling, caching, SSE, or any existing behavior
- Lays groundwork for Phase 2 (cache + SSE integration) without implementing it yet

server/app.js

@@ -19,6 +19,7 @@ const embyRoutes = require('./routes/emby');
 const dashboardRoutes = require('./routes/dashboard');
 const historyRoutes = require('./routes/history');
 const authRoutes = require('./routes/auth');
+const webhookRoutes = require('./routes/webhook');
 const verifyCsrf = require('./middleware/verifyCsrf');
 
 function createApp({ skipRateLimits = false } = {}) {
@@ -94,6 +95,7 @@ function createApp({ skipRateLimits = false } = {}) {
   // API routes
   app.use('/api', apiLimiter);
   app.use('/api/auth', authRoutes);
+  app.use('/api/webhook', webhookRoutes);
 
   // CSRF protection for all state-changing API requests below
   app.use('/api', verifyCsrf);

server/routes/webhook.js

@@ -0,0 +1,89 @@
+// Copyright (c) 2026 Gordon Bolton. MIT License.
+const express = require('express');
+const { logToFile } = require('../utils/logger');
+const { getWebhookSecret } = require('../utils/config');
+
+const router = express.Router();
+
+/**
+ * Validate webhook secret from the X-Sofarr-Webhook-Secret header
+ * @param {Object} req - Express request object
+ * @returns {boolean} True if secret is valid, false otherwise
+ */
+function validateWebhookSecret(req) {
+  const expectedSecret = getWebhookSecret();
+  const providedSecret = req.get('X-Sofarr-Webhook-Secret');
+  
+  if (!expectedSecret) {
+    logToFile('[Webhook] WARNING: SOFARR_WEBHOOK_SECRET not configured, rejecting webhook');
+    return false;
+  }
+  
+  if (!providedSecret) {
+    logToFile('[Webhook] WARNING: Missing X-Sofarr-Webhook-Secret header');
+    return false;
+  }
+  
+  if (providedSecret !== expectedSecret) {
+    logToFile('[Webhook] WARNING: Invalid webhook secret provided');
+    return false;
+  }
+  
+  return true;
+}
+
+/**
+ * POST /api/webhook/sonarr
+ * Receives webhook events from Sonarr instances.
+ * Validates the secret, logs the event, and returns 200 immediately.
+ * 
+ * Phase 1: Receiver only - no cache or SSE integration yet.
+ * Future phases will integrate with PALDRA registry for event-driven updates.
+ */
+router.post('/sonarr', (req, res) => {
+  if (!validateWebhookSecret(req)) {
+    return res.status(401).json({ error: 'Unauthorized' });
+  }
+  
+  try {
+    const { eventType, instanceName } = req.body || {};
+    logToFile(`[Webhook] Sonarr event received - Type: ${eventType || 'unknown'}, Instance: ${instanceName || 'unknown'}`);
+    logToFile(`[Webhook] Sonarr payload: ${JSON.stringify(req.body)}`);
+    
+    // Phase 1: Log and respond immediately
+    // Future phases will push to cache and trigger SSE
+    res.status(200).json({ received: true });
+  } catch (error) {
+    logToFile(`[Webhook] Sonarr error: ${error.message}`);
+    res.status(200).json({ received: true }); // Still return 200 to avoid webhook retries
+  }
+});
+
+/**
+ * POST /api/webhook/radarr
+ * Receives webhook events from Radarr instances.
+ * Validates the secret, logs the event, and returns 200 immediately.
+ * 
+ * Phase 1: Receiver only - no cache or SSE integration yet.
+ * Future phases will integrate with PALDRA registry for event-driven updates.
+ */
+router.post('/radarr', (req, res) => {
+  if (!validateWebhookSecret(req)) {
+    return res.status(401).json({ error: 'Unauthorized' });
+  }
+  
+  try {
+    const { eventType, instanceName } = req.body || {};
+    logToFile(`[Webhook] Radarr event received - Type: ${eventType || 'unknown'}, Instance: ${instanceName || 'unknown'}`);
+    logToFile(`[Webhook] Radarr payload: ${JSON.stringify(req.body)}`);
+    
+    // Phase 1: Log and respond immediately
+    // Future phases will push to cache and trigger SSE
+    res.status(200).json({ received: true });
+  } catch (error) {
+    logToFile(`[Webhook] Radarr error: ${error.message}`);
+    res.status(200).json({ received: true }); // Still return 200 to avoid webhook retries
+  }
+});
+
+module.exports = router;

server/utils/config.js

@@ -114,6 +114,10 @@ function getRtorrentInstances() {
   );
 }
 
+function getWebhookSecret() {
+  return process.env.SOFARR_WEBHOOK_SECRET || '';
+}
+
 module.exports = {
   getSABnzbdInstances,
   getSonarrInstances,
@@ -121,6 +125,7 @@ module.exports = {
   getQbittorrentInstances,
   getTransmissionInstances,
   getRtorrentInstances,
+  getWebhookSecret,
   parseInstances,
   validateInstanceUrl
 };