100 lines
3.9 KiB
Python
100 lines
3.9 KiB
Python
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"""
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Shared-secret middleware that locks the engine to the trusted Java backend.
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Config (resolved via :class:`stirling.config.AppSettings`/pydantic-settings):
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``STIRLING_ENGINE_SHARED_SECRET`` - non-public routes need ``X-Engine-Auth`` or 401.
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``STIRLING_ENGINE_REQUIRE_AUTH`` - fail closed with 503 when truthy and no secret is set.
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"""
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from __future__ import annotations
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import hmac
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import logging
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from collections.abc import Iterable
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from starlette.middleware.base import BaseHTTPMiddleware, RequestResponseEndpoint
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from starlette.requests import Request
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from starlette.responses import JSONResponse, Response
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from starlette.types import ASGIApp
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from stirling.config import load_settings
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logger = logging.getLogger(__name__)
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_HEADER = "X-Engine-Auth"
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# Public paths (liveness + docs); everything else needs the secret when configured.
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_PUBLIC_PREFIXES: tuple[str, ...] = (
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"/health",
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"/docs",
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"/redoc",
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"/openapi.json",
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)
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class EngineSharedSecretMiddleware(BaseHTTPMiddleware):
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"""Reject non-public requests lacking the shared secret.
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Non-public path: secret set -> require matching X-Engine-Auth (else 401); else require flag
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truthy -> 503 (fail-closed); else allow through.
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Secret/require values come from :class:`stirling.config.AppSettings` by default; tests can
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pass them explicitly to avoid touching the lru-cached settings.
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"""
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def __init__(
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self,
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app: ASGIApp,
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public_prefixes: Iterable[str] = _PUBLIC_PREFIXES,
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*,
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secret: str | None = None,
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require: bool | None = None,
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) -> None:
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super().__init__(app)
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self._public_prefixes = tuple(public_prefixes)
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if secret is None or require is None:
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settings = load_settings()
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if secret is None:
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secret = settings.engine_shared_secret
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if require is None:
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require = settings.engine_require_auth
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self._secret = secret or ""
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self._require = bool(require)
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if self._secret:
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logger.info(
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"Engine shared-secret enforcement ENABLED: non-public routes require a valid %s"
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" header (constant-time compared).",
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_HEADER,
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)
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elif self._require:
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logger.error(
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"STIRLING_ENGINE_REQUIRE_AUTH is enabled but STIRLING_ENGINE_SHARED_SECRET is not"
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" set - the engine will REFUSE every non-public request (HTTP 503, fail-closed)"
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" until a shared secret is configured.",
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)
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else:
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logger.warning(
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"STIRLING_ENGINE_SHARED_SECRET not set - engine shared-secret enforcement is"
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" DISABLED. The AI and document routes then trust the caller-supplied X-User-Id"
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" header alone. Set this secret (and STIRLING_ENGINE_REQUIRE_AUTH=true) in any"
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" deployment that exposes the engine beyond localhost.",
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)
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def _is_public(self, path: str) -> bool:
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return any(path == p or path.startswith(p + "/") for p in self._public_prefixes)
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async def dispatch(self, request: Request, call_next: RequestResponseEndpoint) -> Response:
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if not self._is_public(request.url.path):
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if self._secret:
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offered = request.headers.get(_HEADER) or ""
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# Constant-time compare to avoid timing leaks.
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if not hmac.compare_digest(offered, self._secret):
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return JSONResponse({"detail": "Missing or invalid X-Engine-Auth header."}, status_code=401)
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elif self._require:
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# Fail closed: require flag set but no secret configured.
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return JSONResponse(
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{"detail": ("Engine authentication is required but no shared secret is configured.")},
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status_code=503,
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)
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return await call_next(request)
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