172 lines
6.8 KiB
Python
172 lines
6.8 KiB
Python
"""CSRF protection middleware for FastAPI.
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Per RFC-001:
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State-changing operations require CSRF protection.
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"""
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import secrets
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from collections.abc import Callable
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from app.gateway.auth.disabled_mode import is_auth_disabled
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from app.gateway.proxy_path import app_relative_path
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from fastapi import Request, Response
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from starlette.middleware.base import BaseHTTPMiddleware
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from starlette.responses import JSONResponse
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from starlette.types import ASGIApp
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CSRF_COOKIE_NAME = "csrf_token"
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CSRF_HEADER_NAME = "X-CSRF-Token"
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CSRF_TOKEN_LENGTH = 64 # bytes
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def is_secure_request(request: Request) -> bool:
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"""Detect whether the original client request was made over HTTPS."""
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return request.headers.get("x-forwarded-proto", request.url.scheme) == "https"
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def generate_csrf_token() -> str:
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"""Generate a secure random CSRF token."""
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return secrets.token_urlsafe(CSRF_TOKEN_LENGTH)
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def should_check_csrf(request: Request) -> bool:
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"""Determine if a request needs CSRF validation.
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CSRF is checked for state-changing methods (POST, PUT, DELETE, PATCH).
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GET, HEAD, OPTIONS, and TRACE are exempt per RFC 7231.
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"""
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if request.method not in ("POST", "PUT", "DELETE", "PATCH"):
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return False
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# Match the application-relative path so a reverse-proxy prefix
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# (e.g. /xxx/api/v1/auth/me) does not defeat these whitelists.
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path = app_relative_path(request)
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stripped = path.rstrip("/")
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# Exempt /api/v1/auth/me endpoint
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if stripped == "/api/v1/auth/me":
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return False
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# Anonymous public endpoints (mirror auth_middleware._PUBLIC_PATH_PREFIXES).
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# These intentionally have no cookie session, so the Double-Submit Cookie
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# pattern is both impossible (no token to compare) and unnecessary (no
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# session for an attacker to ride). Without this exemption every public
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# PUT/POST returns 403 even though auth was bypassed earlier in the chain.
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if path.startswith("/api/public/"):
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return False
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# 开放问答接口同样是匿名、无会话的(见 auth_middleware._PUBLIC_PATH_PREFIXES),
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# 双提交 Cookie 既无 token 可比、也无会话可被伪造,豁免之。
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if path.startswith("/api/open/"):
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return False
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return True
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_AUTH_EXEMPT_PATHS: frozenset[str] = frozenset(
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{
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"/api/v1/auth/login/local",
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"/api/v1/auth/login/username",
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# Token-exchange login is sessionless on first call (no CSRF cookie yet),
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# exactly like the other login endpoints — mirror auth_middleware's
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# _PUBLIC_EXACT_PATHS, which already whitelists it.
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"/api/v1/auth/login/token",
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"/api/v1/auth/logout",
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"/api/v1/auth/register",
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"/api/v1/auth/initialize",
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# 并行多智能体面板专用取 token 端点（公共 + CSRF 豁免）。
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"/api/parallel-agents/auth/token",
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}
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)
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def is_auth_endpoint(request: Request) -> bool:
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"""Check if the request is to an auth endpoint.
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Auth endpoints don't need CSRF validation on first call (no token).
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Matches the application-relative path so a reverse-proxy prefix does not
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defeat the whitelist.
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"""
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return app_relative_path(request).rstrip("/") in _AUTH_EXEMPT_PATHS
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def _has_bearer_auth(request: Request) -> bool:
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"""Return True when Authorization header carries a Bearer token."""
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authorization = request.headers.get("authorization", "").strip()
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if not authorization:
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return False
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scheme, _, token = authorization.partition(" ")
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return scheme.lower() == "bearer" and bool(token.strip())
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def _has_cookie_session(request: Request) -> bool:
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"""Return True when the request carries a cookie-based session.
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Double-Submit-Cookie CSRF only protects requests the browser authenticates
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**automatically via cookies** — that is the exact surface a cross-site
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forgery can ride. A request with no ``access_token`` session cookie has no
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session for an attacker to exploit, so enforcing CSRF on it is both
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pointless and harmful: a freshly-loaded browser (e.g. one that just cleared
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its cache/cookies) hitting the login endpoint would otherwise be rejected
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with "CSRF token missing" before it can even sign in. Such an
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unauthenticated request, if forged, is rejected by the auth layer (401)
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anyway.
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"""
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return bool(request.cookies.get("access_token"))
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class CSRFMiddleware(BaseHTTPMiddleware):
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"""Middleware that implements CSRF protection using Double Submit Cookie pattern."""
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def __init__(self, app: ASGIApp) -> None:
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super().__init__(app)
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async def dispatch(self, request: Request, call_next: Callable) -> Response:
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_is_auth = is_auth_endpoint(request)
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if is_auth_disabled():
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return await call_next(request)
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# Double-submit-cookie CSRF applies to cookie-based browser sessions.
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# API clients using explicit Bearer tokens are not CSRF-prone, and a
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# request with no session cookie at all (e.g. a fresh browser signing
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# in) has no session to forge — only enforce when an ``access_token``
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# cookie is actually present.
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if should_check_csrf(request) and not _is_auth and not _has_bearer_auth(request) and _has_cookie_session(request):
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cookie_token = request.cookies.get(CSRF_COOKIE_NAME)
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header_token = request.headers.get(CSRF_HEADER_NAME)
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if not cookie_token or not header_token:
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return JSONResponse(
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status_code=403,
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content={"detail": "CSRF token missing. Include X-CSRF-Token header."},
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)
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if not secrets.compare_digest(cookie_token, header_token):
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return JSONResponse(
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status_code=403,
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content={"detail": "CSRF token mismatch."},
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)
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response = await call_next(request)
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# For auth endpoints that set up session, also set CSRF cookie
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if _is_auth and request.method == "POST":
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# Generate a new CSRF token for the session
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csrf_token = generate_csrf_token()
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is_https = is_secure_request(request)
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response.set_cookie(
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key=CSRF_COOKIE_NAME,
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value=csrf_token,
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httponly=False, # Must be JS-readable for Double Submit Cookie pattern
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secure=is_https,
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samesite="strict",
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)
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return response
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def get_csrf_token(request: Request) -> str | None:
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"""Get the CSRF token from the current request's cookies.
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This is useful for server-side rendering where you need to embed
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token in forms or headers.
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"""
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return request.cookies.get(CSRF_COOKIE_NAME)
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