leocrm/app/core/middleware.py

"""CSRF middleware — Origin header + CSRF token validation for state-changing requests."""

from __future__ import annotations

import logging
import re
import uuid as uuid_mod

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 SecurityHeadersMiddleware(BaseHTTPMiddleware):
    """Add security headers to all responses."""

    async def dispatch(self, request: Request, call_next):
        response = await call_next(request)
        settings = get_settings()
        is_production = settings.environment == "production"

        # HSTS — only in production (HTTPS assumed behind proxy)
        if is_production:
            response.headers["Strict-Transport-Security"] = (
                "max-age=63072000; includeSubDomains; preload"
            )

        # Prevent MIME type sniffing
        response.headers["X-Content-Type-Options"] = "nosniff"

        # Prevent clickjacking
        response.headers["X-Frame-Options"] = "DENY"

        # Content Security Policy — restrictive but allows inline styles for SPA
        response.headers["Content-Security-Policy"] = (
            "default-src 'self'; "
            "script-src 'self'; "
            "style-src 'self' 'unsafe-inline' https://fonts.googleapis.com; "
            "img-src 'self' data: blob:; "
            "font-src 'self' https://fonts.gstatic.com; "
            "connect-src 'self' wss: ws:; "
            "frame-ancestors 'none'; "
            "base-uri 'self'; "
            "form-action 'self'"
        )

        # Referrer policy
        response.headers["Referrer-Policy"] = "strict-origin-when-cross-origin"

        # Permissions policy
        response.headers["Permissions-Policy"] = (
            "geolocation=(), microphone=(), camera=()"
        )

        return response


class CSRFMiddleware(BaseHTTPMiddleware):
    """Validate Origin header and CSRF token on all state-changing requests.

    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):
        # Skip WebSocket upgrade requests — they use GET and are handled separately
        if request.headers.get("upgrade", "").lower() == "websocket":
            return await call_next(request)

        # Bearer-token requests are CSRF-immune by design: the Authorization
        # header is never attached automatically by browsers, so cross-site
        # requests cannot forge it. Exempts programmatic API clients
        # (external agent API, MCP, integrations) from Origin+CSRF checks —
        # they authenticate via get_current_user_bearer instead.
        auth_header = request.headers.get("authorization", "")
        if auth_header.startswith("Bearer "):
            return await call_next(request)

        if request.method in self.UNSAFE_METHODS:
            # 1. Origin header check
            origin = request.headers.get("origin")
            if not origin:
                return JSONResponse(
                    status_code=status.HTTP_403_FORBIDDEN,
                    content={"detail": "Missing Origin header", "code": "csrf_missing_origin"},
                )

            settings = get_settings()
            allowed = settings.cors_origin_list
            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 path.endswith("/guest/login") or path.endswith("/guest/logout") or path.endswith("/password-reset/request") or path.endswith("/password-reset/confirm") or path.endswith("/api/v1/errors") or path == "/api/v1/errors":
                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 session (Redis with DB fallback)
            from app.core.auth import get_redis, get_session_data

            redis = get_redis()
            session_data = await get_session_data(redis, session_id)
            if session_data is None:
                return JSONResponse(
                    status_code=status.HTTP_403_FORBIDDEN,
                    content={"detail": "Session expired for CSRF validation", "code": "csrf_session_expired"},
                )

            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"},
                )

            # Sliding session: also extend TTL on CSRF-validated unsafe requests
            # (best-effort — ignore Redis errors during outage)
            try:
                await redis.expire(f"session:{session_id}", settings.session_ttl_seconds)
            except Exception:
                pass

        return await call_next(request)


class AuditMiddleware(BaseHTTPMiddleware):
    """Safety-net audit trail for ALL successful mutating requests.

    AGENTS.md requires every mutation to produce an audit entry. Explicit
    ``log_audit`` calls in routes/services remain the detail layer (entity ids,
    change diffs); this middleware guarantees a baseline entry for mutations
    that lack one, marked with ``source=middleware`` in ``details``.

    Best-effort by design: audit failures never break the request.
    """

    _MUTATING = {"POST", "PUT", "PATCH", "DELETE"}
    _SKIP_PREFIXES = (
        "/api/v1/auth",
        "/api/v1/health",
        "/api/v1/errors",
        "/api/v1/audit",
        "/api/v1/external",
    )

    async def dispatch(self, request: Request, call_next):
        response = await call_next(request)

        if request.method not in self._MUTATING:
            return response
        if response.status_code < 200 or response.status_code >= 300:
            return response
        path = request.url.path
        if any(path.startswith(p) for p in self._SKIP_PREFIXES):
            return response

        try:
            await self._write_entry(request, path, response.status_code)
        except Exception:
            logging.getLogger(__name__).debug(
                "AuditMiddleware: failed to write baseline entry for %s %s", request.method, path
            )
        return response

    @staticmethod
    def _derive_entity_type(path: str) -> str:
        """Derive an entity_type from the second URL segment."""
        parts = [p for p in path.split("/") if p]
        # /api/v1/<resource>/... -> resource; singularize naive trailing 's'
        resource = parts[2] if len(parts) > 2 and parts[0] == "api" and parts[1] == "v1" else (parts[0] if parts else "unknown")
        return resource[:-1] if len(resource) > 3 and resource.endswith("s") else resource

    async def _write_entry(self, request: Request, path: str, status_code: int) -> None:
        from app.core.audit import log_audit
        from app.core.auth import get_redis, get_session_data
        from app.core.db import create_db_session

        # Attribute via the Redis session (same source as CSRFMiddleware) —
        # FastAPI dependencies run after middleware, so request.state is empty here.
        settings = get_settings()
        session_id = request.cookies.get(settings.session_cookie_name)
        if not session_id:
            return  # unauthenticated — nothing to attribute
        redis = get_redis()
        session_data = await get_session_data(redis, session_id)
        if not session_data:
            return
        tenant_raw = session_data.get("tenant_id")
        user_raw = session_data.get("user_id")
        if not tenant_raw:
            return

        action_map = {"POST": "create", "PATCH": "update", "PUT": "update", "DELETE": "delete"}
        entity_id: uuid_mod.UUID | None = None
        parts = [p for p in path.split("/") if p]
        if parts and re.fullmatch(r"[0-9a-fA-F-]{36}", parts[-1]):
            try:
                entity_id = uuid_mod.UUID(parts[-1])
            except ValueError:
                entity_id = None

        async with create_db_session(uuid_mod.UUID(tenant_raw)) as db:
            await log_audit(
                db,
                uuid_mod.UUID(tenant_raw),
                uuid_mod.UUID(user_raw) if user_raw else None,
                action_map.get(request.method, request.method.lower()),
                self._derive_entity_type(path),
                entity_id,
                changes={
                    "source": "middleware",
                    "method": request.method,
                    "path": path,
                    "status": status_code,
                },
            )
            await db.commit()