B3: CSRF middleware — add X-CSRF-Token validation via Redis session lookup

app/core/middleware.py

@@ -1,23 +1,32 @@
-"""CSRF middleware — Origin header validation for POST/PATCH/DELETE."""
+"""CSRF middleware — Origin header + CSRF token validation for state-changing requests."""
 
 from __future__ import annotations
 
+import json
+import logging
+
 from fastapi import Request, status
 from starlette.middleware.base import BaseHTTPMiddleware
 from starlette.responses import JSONResponse
 
 from app.config import get_settings
 
+logger = logging.getLogger(__name__)
+
 
 class CSRFMiddleware(BaseHTTPMiddleware):
-    """Validate Origin header on all state-changing requests.
+    """Validate Origin header and CSRF token on all state-changing requests.
-    SameSite=Strict cookie + Origin validation = CSRF protection.
+
+    SameSite=Strict cookie + Origin validation + double-submit CSRF token.
+    The CSRF token is generated at login and stored in the Redis session.
+    The client must send it via the X-CSRF-Token header on unsafe methods.
     """
 
     UNSAFE_METHODS = {"POST", "PATCH", "PUT", "DELETE"}
 
     async def dispatch(self, request: Request, call_next):
         if request.method in self.UNSAFE_METHODS:
+            # 1. Origin header check
             origin = request.headers.get("origin")
             if not origin:
                 return JSONResponse(
@@ -27,11 +36,54 @@ class CSRFMiddleware(BaseHTTPMiddleware):
 
             settings = get_settings()
             allowed = settings.cors_origin_list
-            # In production, same-origin is enforced; in dev, explicit origins
             if origin not in allowed:
                 return JSONResponse(
                     status_code=status.HTTP_403_FORBIDDEN,
                     content={"detail": "Invalid Origin", "code": "csrf_invalid_origin"},
                 )
 
+            # 2. CSRF token validation (double-submit pattern)
+            # Skip CSRF token check for auth endpoints (login/password-reset)
+            path = request.url.path
+            if path.endswith("/auth/login") or path.endswith("/auth/logout") or "/password-reset" in path:
+                return await call_next(request)
+
+            csrf_header = request.headers.get("x-csrf-token")
+            if not csrf_header:
+                return JSONResponse(
+                    status_code=status.HTTP_403_FORBIDDEN,
+                    content={"detail": "Missing X-CSRF-Token header", "code": "csrf_missing_token"},
+                )
+
+            # Get session ID from cookie to look up stored CSRF token
+            session_id = request.cookies.get(settings.session_cookie_name)
+            if not session_id:
+                return JSONResponse(
+                    status_code=status.HTTP_403_FORBIDDEN,
+                    content={"detail": "No session for CSRF validation", "code": "csrf_no_session"},
+                )
+
+            # Look up CSRF token from Redis session
+            import redis.asyncio as aioredis
+
+            redis = aioredis.from_url(settings.redis_url, decode_responses=True)
+            try:
+                raw = await redis.get(f"session:{session_id}")
+                if raw is None:
+                    return JSONResponse(
+                        status_code=status.HTTP_403_FORBIDDEN,
+                        content={"detail": "Session expired for CSRF validation", "code": "csrf_session_expired"},
+                    )
+
+                session_data = json.loads(raw)
+                stored_token = session_data.get("csrf_token")
+
+                if not stored_token or stored_token != csrf_header:
+                    return JSONResponse(
+                        status_code=status.HTTP_403_FORBIDDEN,
+                        content={"detail": "CSRF token mismatch", "code": "csrf_token_mismatch"},
+                    )
+            finally:
+                await redis.close()
+
         return await call_next(request)