llama-stack-mirror/llama_stack/distribution/server/auth.py

# Copyright (c) Meta Platforms, Inc. and affiliates.
# All rights reserved.
#
# This source code is licensed under the terms described in the LICENSE file in
# the root directory of this source tree.

import json

import httpx
from aiohttp import hdrs

from llama_stack.distribution.datatypes import AuthenticationConfig, User
from llama_stack.distribution.request_headers import user_from_scope
from llama_stack.distribution.server.auth_providers import create_auth_provider
from llama_stack.distribution.server.routes import find_matching_route, initialize_route_impls
from llama_stack.log import get_logger

logger = get_logger(name=__name__, category="auth")


class AuthenticationMiddleware:
    """Middleware that authenticates requests using configured authentication provider.

    This middleware:
    1. Extracts the Bearer token from the Authorization header
    2. Uses the configured auth provider to validate the token
    3. Extracts user attributes from the provider's response
    4. Makes these attributes available to the route handlers for access control

    The middleware supports multiple authentication providers through the AuthProvider interface:
    - Kubernetes: Validates tokens against the Kubernetes API server
    - Custom: Validates tokens against a custom endpoint

    Authentication Request Format for Custom Auth Provider:
    ```json
    {
        "api_key": "the-api-key-extracted-from-auth-header",
        "request": {
            "path": "/models/list",
            "headers": {
                "content-type": "application/json",
                "user-agent": "..."
                // All headers except Authorization
            },
            "params": {
                "limit": ["100"],
                "offset": ["0"]
                // Query parameters as key -> list of values
            }
        }
    }
    ```

    Expected Auth Endpoint Response Format:
    ```json
    {
        "access_attributes": {    // Structured attribute format
            "roles": ["admin", "user"],
            "teams": ["ml-team", "nlp-team"],
            "projects": ["llama-3", "project-x"],
            "namespaces": ["research"]
        },
        "message": "Optional message about auth result"
    }
    ```

    Token Validation:
    Each provider implements its own token validation logic:
    - Kubernetes: Uses TokenReview API to validate service account tokens
    - Custom: Sends token to custom endpoint for validation

    Attribute-Based Access Control:
    The attributes returned by the auth provider are used to determine which
    resources the user can access. Resources can specify required attributes
    using the access_attributes field. For a user to access a resource:

    1. All attribute categories specified in the resource must be present in the user's attributes
    2. For each category, the user must have at least one matching value

    If the auth provider doesn't return any attributes, the user will only be able to
    access resources that don't have access_attributes defined.
    """

    def __init__(self, app, auth_config: AuthenticationConfig, impls):
        self.app = app
        self.impls = impls
        self.auth_provider = create_auth_provider(auth_config)

    async def __call__(self, scope, receive, send):
        if scope["type"] == "http":
            # First, handle authentication
            headers = dict(scope.get("headers", []))
            auth_header = headers.get(b"authorization", b"").decode()

            if not auth_header:
                error_msg = self.auth_provider.get_auth_error_message(scope)
                return await self._send_auth_error(send, error_msg)

            if not auth_header.startswith("Bearer "):
                return await self._send_auth_error(send, "Invalid Authorization header format")

            token = auth_header.split("Bearer ", 1)[1]

            # Validate token and get access attributes
            try:
                validation_result = await self.auth_provider.validate_token(token, scope)
            except httpx.TimeoutException:
                logger.exception("Authentication request timed out")
                return await self._send_auth_error(send, "Authentication service timeout")
            except ValueError as e:
                logger.exception("Error during authentication")
                return await self._send_auth_error(send, str(e))
            except Exception:
                logger.exception("Error during authentication")
                return await self._send_auth_error(send, "Authentication service error")

            # Store the client ID in the request scope so that downstream middleware (like QuotaMiddleware)
            # can identify the requester and enforce per-client rate limits.
            scope["authenticated_client_id"] = token

            # Store attributes in request scope
            scope["principal"] = validation_result.principal
            if validation_result.attributes:
                scope["user_attributes"] = validation_result.attributes
            logger.debug(
                f"Authentication successful: {validation_result.principal} with {len(validation_result.attributes)} attributes"
            )

            # Scope-based API access control
            path = scope.get("path", "")
            method = scope.get("method", hdrs.METH_GET)

            if not hasattr(self, "route_impls"):
                self.route_impls = initialize_route_impls(self.impls)

            try:
                _, _, _, webmethod = find_matching_route(method, path, self.route_impls)
            except ValueError:
                # If no matching endpoint is found, pass through to FastAPI
                return await self.app(scope, receive, send)

            if webmethod.required_scope:
                user = user_from_scope(scope)
                if not _has_required_scope(webmethod.required_scope, user):
                    return await self._send_auth_error(
                        send,
                        f"Access denied: user does not have required scope: {webmethod.required_scope}",
                        status=403,
                    )

        return await self.app(scope, receive, send)

    async def _send_auth_error(self, send, message, status=401):
        await send(
            {
                "type": "http.response.start",
                "status": status,
                "headers": [[b"content-type", b"application/json"]],
            }
        )
        error_key = "message" if status == 401 else "detail"
        error_msg = json.dumps({"error": {error_key: message}}).encode()
        await send({"type": "http.response.body", "body": error_msg})


def _has_required_scope(required_scope: str, user: User | None) -> bool:
    # if no user, assume auth is not enabled
    if not user:
        return True

    if not user.attributes:
        return False

    user_scopes = user.attributes.get("scopes", [])
    return required_scope in user_scopes