feat(bot): support random token in signature verification

- Enhanced signature verification by adding support for a `random` token included in webhook headers.
- Introduced logging to display signature variants for debugging purposes.
- Improved webhook handling to process new `X-Nextcloud-Talk-Random` header.

systems/x86_64-linux/mx/nextcloud-claude-bot/bot.py

@@ -56,25 +56,37 @@ conversations: dict[str, list[tuple[datetime, str, str]]] = {}
 MAX_HISTORY = 10  # Keep last N exchanges per user
 
 
-def verify_signature(body: bytes, signature: str) -> bool:
+def verify_signature(body: bytes, signature: str, random: Optional[str] = None) -> bool:
     """Verify Nextcloud webhook signature."""
     if not BOT_SECRET:
         log.warning("No bot secret configured, skipping signature verification")
         return True
 
-    expected = hmac.new(
-        BOT_SECRET.encode(),
-        body,
-        hashlib.sha256
-    ).hexdigest()
-
     # Nextcloud sends: sha256=<hex>
     if signature.startswith("sha256="):
         signature = signature[7:]
 
-    log.info(f"Signature verification: secret_len={len(BOT_SECRET)}, expected={expected[:16]}..., received={signature[:16]}...")
+    # Try different signature computation methods
+    # Method 1: Just body
+    expected1 = hmac.new(BOT_SECRET.encode(), body, hashlib.sha256).hexdigest()
 
-    return hmac.compare_digest(expected, signature)
+    # Method 2: random + body (if random header present)
+    if random:
+        expected2 = hmac.new(BOT_SECRET.encode(), (random.encode() + body), hashlib.sha256).hexdigest()
+    else:
+        expected2 = None
+
+    log.info(f"Signature verification: received={signature[:16]}...")
+    log.info(f"  Method 1 (body only): {expected1[:16]}...")
+    if expected2:
+        log.info(f"  Method 2 (random+body): {expected2[:16]}...")
+
+    if hmac.compare_digest(expected1, signature):
+        return True
+    if expected2 and hmac.compare_digest(expected2, signature):
+        return True
+
+    return False
 
 
 def build_prompt(user_id: str, message: str) -> str:
@@ -182,12 +194,16 @@ async def send_reply(conversation_token: str, message: str, reply_to: int = None
 async def handle_webhook(
     request: Request,
     x_nextcloud_talk_signature: Optional[str] = Header(None, alias="X-Nextcloud-Talk-Signature"),
+    x_nextcloud_talk_random: Optional[str] = Header(None, alias="X-Nextcloud-Talk-Random"),
 ):
     """Handle incoming webhook from Nextcloud Talk."""
     body = await request.body()
 
+    log.info(f"Headers: signature={x_nextcloud_talk_signature}, random={x_nextcloud_talk_random}")
+    log.info(f"Body (first 200): {body[:200]}")
+
     # Verify signature
-    if x_nextcloud_talk_signature and not verify_signature(body, x_nextcloud_talk_signature):
+    if x_nextcloud_talk_signature and not verify_signature(body, x_nextcloud_talk_signature, x_nextcloud_talk_random):
         log.warning("Invalid webhook signature")
         raise HTTPException(status_code=401, detail="Invalid signature")