security: v1.7.7 hardening release

- Add WEBHOOK_CLIENT_SECRET validation for Graph webhooks
- Add Redis-backed rate limiting (fetch/ask/write/default tiers)
- Validate LLM_BASE_URL to prevent SSRF (HTTPS only, block private IPs)
- Enforce non-wildcard CORS when AUTH_ENABLED=true
- Add Content-Security-Policy headers
- Fix audit middleware to use verified JWT claims via contextvars
- Cap bulk_tags updates to 10,000 documents
- Return generic error messages to clients (no internal detail leakage)
- Strict AlertCondition Pydantic model for alert rules
- Security warning on MCP stdio server startup
- Remove MongoDB/Redis host ports from docker-compose
- Remove mongo_query from /ask API response

backend/rate_limiter.py

@@ -0,0 +1,82 @@
+"""Simple Redis-backed fixed-window rate limiter."""
+
+import time
+
+import structlog
+from config import RATE_LIMIT_ENABLED, RATE_LIMIT_REQUESTS, RATE_LIMIT_WINDOW_SECONDS
+from fastapi import HTTPException, Request
+from redis_client import get_redis
+
+logger = structlog.get_logger("aoc.rate_limit")
+
+
+class RateLimitExceeded(HTTPException):
+    def __init__(self, retry_after: int):
+        super().__init__(
+            status_code=429,
+            detail="Rate limit exceeded. Please slow down.",
+            headers={"Retry-After": str(retry_after)},
+        )
+
+
+def _get_identifier(request: Request) -> str:
+    """Best-effort client identifier: authenticated sub, or X-Forwarded-For, or client host."""
+    user = getattr(request.state, "user", None)
+    if user and isinstance(user, dict):
+        sub = user.get("sub")
+        if sub and sub != "anonymous":
+            return f"user:{sub}"
+
+    forwarded = request.headers.get("x-forwarded-for")
+    if forwarded:
+        return f"ip:{forwarded.split(',')[0].strip()}"
+
+    return f"ip:{request.client.host if request.client else 'unknown'}"
+
+
+def _get_path_category(path: str) -> str:
+    """Bucket paths into rate-limit categories."""
+    if path.startswith("/api/fetch"):
+        return "fetch"
+    if path.startswith("/api/ask"):
+        return "ask"
+    if path.startswith("/api/events/bulk-tags"):
+        return "write"
+    return "default"
+
+
+def _limit_for_category(category: str) -> tuple[int, int]:
+    """Return (max_requests, window_seconds) for a category."""
+    if category == "fetch":
+        return (10, 3600)  # 10 per hour
+    if category == "ask":
+        return (30, 60)  # 30 per minute
+    if category == "write":
+        return (20, 60)  # 20 per minute
+    return (RATE_LIMIT_REQUESTS, RATE_LIMIT_WINDOW_SECONDS)
+
+
+async def check_rate_limit(request: Request):
+    """Raise RateLimitExceeded if the client has exceeded their quota."""
+    if not RATE_LIMIT_ENABLED:
+        return
+
+    category = _get_path_category(request.url.path)
+    limit, window = _limit_for_category(category)
+
+    identifier = _get_identifier(request)
+    now = int(time.time())
+    window_key = now // window
+    redis_key = f"rate_limit:{identifier}:{category}:{window_key}"
+
+    try:
+        redis = await get_redis()
+        count = await redis.incr(redis_key)
+        if count == 1:
+            await redis.expire(redis_key, window)
+        if count > limit:
+            raise RateLimitExceeded(retry_after=window - (now % window))
+    except RateLimitExceeded:
+        raise
+    except Exception as exc:
+        logger.warning("Rate limiter Redis error; allowing request", error=str(exc))