Fix 7 critical security bugs and 1 high-severity data loss bug

- CSRF: HMAC-signed double-submit cookie (server-bound, not raw compare)
- Keychain: execFileSync with arg arrays to prevent command injection
- Caddy config: always use structured generation, never accept raw config
- Templates: replace {{GENERATED_SECRET}} with crypto.randomBytes
- Caddyfile removal: move regex inside ctx.caddy.modify() to fix TOCTOU race
- Credentials: proper-lockfile for all file operations, fix key rotation
  to decrypt with old key before generating new key
- Service removal: filter by ID only, not AND with appTemplate

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

dashcaddy-api/crypto-utils.js

@@ -267,6 +267,51 @@ function writeEncryptedFile(filePath, credentials, sensitiveFields = ['password'
   console.log(`[Crypto] Saved encrypted credentials to ${filePath}`);
 }
 
+/**
+ * Rotate the encryption key — generates a new key and returns both old and new
+ * @returns {{ oldKey: Buffer, newKey: Buffer }} Old and new key pair
+ * @throws {Error} If new key cannot be saved to disk
+ */
+function rotateKey() {
+  const oldKey = loadOrCreateKey(); // Ensure we have the current key loaded
+  const newKey = generateKey();
+
+  try {
+    fs.writeFileSync(KEY_FILE, newKey.toString('hex'), { mode: 0o600 });
+  } catch (error) {
+    throw new Error(`Failed to save new encryption key: ${error.message}`);
+  }
+
+  // Only update the cached key after file write succeeds
+  encryptionKey = newKey;
+  return { oldKey, newKey };
+}
+
+/**
+ * Decrypt data using a specific key (for key rotation)
+ * @param {string} encryptedData - Encrypted string in format iv:authTag:ciphertext
+ * @param {Buffer} key - The key to decrypt with
+ * @returns {string} Decrypted plaintext
+ */
+function decryptWithKey(encryptedData, key) {
+  const parts = encryptedData.split(':');
+  if (parts.length !== 3) {
+    throw new Error('Invalid encrypted data format');
+  }
+
+  const iv = Buffer.from(parts[0], 'base64');
+  const authTag = Buffer.from(parts[1], 'base64');
+  const ciphertext = parts[2];
+
+  const decipher = crypto.createDecipheriv(ALGORITHM, key, iv);
+  decipher.setAuthTag(authTag);
+
+  let decrypted = decipher.update(ciphertext, 'base64', 'utf8');
+  decrypted += decipher.final('utf8');
+
+  return decrypted;
+}
+
 // Initialize key on module load
 loadOrCreateKey();
 
@@ -280,5 +325,7 @@ module.exports = {
   readEncryptedFile,
   writeEncryptedFile,
   loadOrCreateKey,
-  deriveKey
+  deriveKey,
+  rotateKey,
+  decryptWithKey
 };