deer-flow/backend/app/gateway/authz.py

"""Authorization decorators and context for DeerFlow.

Inspired by LangGraph Auth system: https://github.com/langchain-ai/langgraph/blob/main/libs/sdk-py/langgraph_sdk/auth/__init__.py

**Usage:**

1. Use ``@require_auth`` on routes that need authentication
2. Use ``@require_permission("resource", "action", filter_key=...)`` for permission checks
3. The decorator chain processes from bottom to top

**Example:**

    @router.get("/{thread_id}")
    @require_auth
    @require_permission("threads", "read", owner_check=True)
    async def get_thread(thread_id: str, request: Request):
        # User is authenticated and has threads:read permission
        ...

**Permission Model:**

- threads:read   - View thread
- threads:write  - Create/update thread
- threads:delete - Delete thread
- runs:create   - Run agent
- runs:read     - View run
- runs:cancel   - Cancel run
"""

from __future__ import annotations

import functools
from collections.abc import Callable
from typing import TYPE_CHECKING, Any, ParamSpec, TypeVar

from fastapi import HTTPException, Request

if TYPE_CHECKING:
    from app.gateway.auth.models import User

P = ParamSpec("P")
T = TypeVar("T")


# Permission constants
class Permissions:
    """Permission constants for resource:action format."""

    # Threads
    THREADS_READ = "threads:read"
    THREADS_WRITE = "threads:write"
    THREADS_DELETE = "threads:delete"

    # Runs
    RUNS_CREATE = "runs:create"
    RUNS_READ = "runs:read"
    RUNS_CANCEL = "runs:cancel"


class AuthContext:
    """Authentication context for the current request.

    Stored in request.state.auth after require_auth decoration.

    Attributes:
        user: The authenticated user, or None if anonymous
        permissions: List of permission strings (e.g., "threads:read")
    """

    __slots__ = ("user", "permissions")

    def __init__(self, user: User | None = None, permissions: list[str] | None = None):
        self.user = user
        self.permissions = permissions or []

    @property
    def is_authenticated(self) -> bool:
        """Check if user is authenticated."""
        return self.user is not None

    def has_permission(self, resource: str, action: str) -> bool:
        """Check if context has permission for resource:action.

        Args:
            resource: Resource name (e.g., "threads")
            action: Action name (e.g., "read")

        Returns:
            True if user has permission
        """
        permission = f"{resource}:{action}"
        return permission in self.permissions

    def require_user(self) -> User:
        """Get user or raise 401.

        Raises:
            HTTPException 401 if not authenticated
        """
        if not self.user:
            raise HTTPException(status_code=401, detail="Authentication required")
        return self.user


def get_auth_context(request: Request) -> AuthContext | None:
    """Get AuthContext from request state."""
    return getattr(request.state, "auth", None)


_ALL_PERMISSIONS: list[str] = [
    Permissions.THREADS_READ,
    Permissions.THREADS_WRITE,
    Permissions.THREADS_DELETE,
    Permissions.RUNS_CREATE,
    Permissions.RUNS_READ,
    Permissions.RUNS_CANCEL,
]


async def _authenticate(request: Request) -> AuthContext:
    """Authenticate request and return AuthContext.

    Delegates to deps.get_optional_user_from_request() for the JWT→User pipeline.
    Returns AuthContext with user=None for anonymous requests.
    """
    from app.gateway.deps import get_optional_user_from_request

    user = await get_optional_user_from_request(request)
    if user is None:
        return AuthContext(user=None, permissions=[])

    # In future, permissions could be stored in user record
    return AuthContext(user=user, permissions=_ALL_PERMISSIONS)


def require_auth[**P, T](func: Callable[P, T]) -> Callable[P, T]:
    """Decorator that authenticates the request and sets AuthContext.

    Must be placed ABOVE other decorators (executes after them).

    Usage:
        @router.get("/{thread_id}")
        @require_auth  # Bottom decorator (executes first after permission check)
        @require_permission("threads", "read")
        async def get_thread(thread_id: str, request: Request):
            auth: AuthContext = request.state.auth
            ...

    Raises:
        ValueError: If 'request' parameter is missing
    """

    @functools.wraps(func)
    async def wrapper(*args: Any, **kwargs: Any) -> Any:
        request = kwargs.get("request")
        if request is None:
            raise ValueError("require_auth decorator requires 'request' parameter")

        # Authenticate and set context
        auth_context = await _authenticate(request)
        request.state.auth = auth_context

        return await func(*args, **kwargs)

    return wrapper


def require_permission(
    resource: str,
    action: str,
    owner_check: bool = False,
    require_existing: bool = False,
) -> Callable[[Callable[P, T]], Callable[P, T]]:
    """Decorator that checks permission for resource:action.

    Must be used AFTER @require_auth.

    Args:
        resource: Resource name (e.g., "threads", "runs")
        action: Action name (e.g., "read", "write", "delete")
        owner_check: If True, validates that the current user owns the resource.
                     Requires 'thread_id' path parameter and performs ownership check.
        require_existing: Only meaningful with ``owner_check=True``. If True, a
                          missing ``threads_meta`` row counts as a denial (404)
                          instead of "untracked legacy thread, allow". Use on
                          **destructive / mutating** routes (DELETE, PATCH,
                          state-update) so a deleted thread can't be re-targeted
                          by another user via the missing-row code path.

    Usage:
        # Read-style: legacy untracked threads are allowed
        @require_permission("threads", "read", owner_check=True)
        async def get_thread(thread_id: str, request: Request):
            ...

        # Destructive: thread row MUST exist and be owned by caller
        @require_permission("threads", "delete", owner_check=True, require_existing=True)
        async def delete_thread(thread_id: str, request: Request):
            ...

    Raises:
        HTTPException 401: If authentication required but user is anonymous
        HTTPException 403: If user lacks permission
        HTTPException 404: If owner_check=True but user doesn't own the thread
        ValueError: If owner_check=True but 'thread_id' parameter is missing
    """

    def decorator(func: Callable[P, T]) -> Callable[P, T]:
        @functools.wraps(func)
        async def wrapper(*args: Any, **kwargs: Any) -> Any:
            request = kwargs.get("request")
            if request is None:
                raise ValueError("require_permission decorator requires 'request' parameter")

            auth: AuthContext = getattr(request.state, "auth", None)
            if auth is None:
                auth = await _authenticate(request)
                request.state.auth = auth

            if not auth.is_authenticated:
                raise HTTPException(status_code=401, detail="Authentication required")

            # Check permission
            if not auth.has_permission(resource, action):
                raise HTTPException(
                    status_code=403,
                    detail=f"Permission denied: {resource}:{action}",
                )

            # Owner check for thread-specific resources.
            #
            # 2.0-rc moved thread metadata into the SQL persistence layer
            # (``threads_meta`` table). We verify ownership via
            # ``ThreadMetaStore.check_access``: it returns True for
            # missing rows (untracked legacy thread) and for rows whose
            # ``user_id`` is NULL (shared / pre-auth data), so this is
            # strict-deny rather than strict-allow — only an *existing*
            # row with a *different* user_id triggers 404.
            if owner_check:
                thread_id = kwargs.get("thread_id")
                if thread_id is None:
                    raise ValueError("require_permission with owner_check=True requires 'thread_id' parameter")

                from app.gateway.deps import get_thread_store

                thread_store = get_thread_store(request)
                allowed = await thread_store.check_access(
                    thread_id,
                    str(auth.user.id),
                    require_existing=require_existing,
                )
                if not allowed:
                    raise HTTPException(
                        status_code=404,
                        detail=f"Thread {thread_id} not found",
                    )

            return await func(*args, **kwargs)

        return wrapper

    return decorator