auth.py

"""Authentication for HTTP component."""

from __future__ import annotations

from collections.abc import Awaitable, Callable
from datetime import timedelta
from ipaddress import ip_address
import logging
import secrets
import time
from typing import Any, Final

from aiohttp import hdrs
from aiohttp.web import (
    Application,
    HTTPInternalServerError,
    Request,
    StreamResponse,
    middleware,
)
import jwt
from jwt import api_jws
from yarl import URL

from homeassistant.auth import jwt_wrapper
from homeassistant.auth.const import GROUP_ID_READ_ONLY
from homeassistant.auth.models import User
from homeassistant.components import websocket_api
from homeassistant.const import HASSIO_USER_NAME
from homeassistant.core import HomeAssistant, callback
from homeassistant.helpers.http import current_request
from homeassistant.helpers.json import json_bytes
from homeassistant.helpers.network import is_cloud_connection
from homeassistant.helpers.storage import Store
from homeassistant.util.network import is_local

from .const import (
    KEY_AUTHENTICATED,
    KEY_HASS_REFRESH_TOKEN_ID,
    KEY_HASS_USER,
    is_supervisor_unix_socket_request,
)

_LOGGER = logging.getLogger(__name__)

DATA_API_PASSWORD: Final = "api_password"
DATA_SIGN_SECRET: Final = "http.auth.sign_secret"
SIGN_QUERY_PARAM: Final = "authSig"
SAFE_QUERY_PARAMS: Final = frozenset(("height", "width"))

STORAGE_VERSION = 1
STORAGE_KEY = "http.auth"
CONTENT_USER_NAME = "Home Assistant Content"


@callback
def async_sign_path(
    hass: HomeAssistant,
    path: str,
    expiration: timedelta,
    *,
    refresh_token_id: str | None = None,
    use_content_user: bool = False,
) -> str:
    """Sign a path for temporary access without auth header."""
    if (secret := hass.data.get(DATA_SIGN_SECRET)) is None:
        secret = hass.data[DATA_SIGN_SECRET] = secrets.token_hex()

    if refresh_token_id is None:
        if use_content_user:
            refresh_token_id = hass.data[STORAGE_KEY]
        elif (
            connection := websocket_api.current_connection.get()
        ) and connection.refresh_token_id:
            refresh_token_id = connection.refresh_token_id
        elif (
            request := current_request.get()
        ) and KEY_HASS_REFRESH_TOKEN_ID in request:
            refresh_token_id = request[KEY_HASS_REFRESH_TOKEN_ID]
        else:
            refresh_token_id = hass.data[STORAGE_KEY]

    url = URL(path)
    now_timestamp = int(time.time())
    expiration_timestamp = now_timestamp + int(expiration.total_seconds())
    params = [itm for itm in url.query.items() if itm[0] not in SAFE_QUERY_PARAMS]
    json_payload = json_bytes(
        {
            "iss": refresh_token_id,
            "path": url.path,
            "params": params,
            "iat": now_timestamp,
            "exp": expiration_timestamp,
        }
    )
    encoded = api_jws.encode(json_payload, secret, "HS256")
    params.append((SIGN_QUERY_PARAM, encoded))
    url = url.with_query(params)
    return f"{url.path}?{url.query_string}"


@callback
def async_user_not_allowed_do_auth(
    hass: HomeAssistant, user: User, request: Request | None = None
) -> str | None:
    """Validate that user is not allowed to do auth things."""
    if not user.is_active:
        return "User is not active"

    if not user.local_only:
        return None

    # User is marked as local only, check if they are allowed to do auth
    if request is None:
        request = current_request.get()

    if not request:
        return "No request available to validate local access"

    if is_cloud_connection(hass):
        return "User is local only"

    try:
        remote_address = ip_address(request.remote)  # type: ignore[arg-type]
    except ValueError:
        return "Invalid remote IP"

    if is_local(remote_address):
        return None

    return "User cannot authenticate remotely"


async def async_setup_auth(  # noqa: C901
    hass: HomeAssistant,
    app: Application,
) -> None:
    """Create auth middleware for the app."""
    store = Store[dict[str, Any]](hass, STORAGE_VERSION, STORAGE_KEY)
    if (data := await store.async_load()) is None:
        data = {}

    refresh_token = None
    if "content_user" in data:
        user = await hass.auth.async_get_user(data["content_user"])
        if user and user.refresh_tokens:
            refresh_token = list(user.refresh_tokens.values())[0]

    if refresh_token is None:
        user = await hass.auth.async_create_system_user(
            CONTENT_USER_NAME, group_ids=[GROUP_ID_READ_ONLY]
        )
        refresh_token = await hass.auth.async_create_refresh_token(user)
        data["content_user"] = user.id
        await store.async_save(data)

    hass.data[STORAGE_KEY] = refresh_token.id

    @callback
    def async_validate_auth_header(request: Request) -> bool:
        """Test authorization header against access token.

        Basic auth_type is legacy code, should be removed with api_password.
        """
        try:
            auth_type, auth_val = request.headers.get(hdrs.AUTHORIZATION, "").split(
                " ", 1
            )
        except ValueError:
            # If no space in authorization header
            return False

        if auth_type != "Bearer":
            return False

        refresh_token = hass.auth.async_validate_access_token(auth_val)

        if refresh_token is None:
            return False

        if async_user_not_allowed_do_auth(hass, refresh_token.user, request):
            return False

        request[KEY_HASS_USER] = refresh_token.user
        request[KEY_HASS_REFRESH_TOKEN_ID] = refresh_token.id
        return True

    @callback
    def async_validate_signed_request(request: Request) -> bool:
        """Validate a signed request."""
        if (secret := hass.data.get(DATA_SIGN_SECRET)) is None:
            return False

        if (signature := request.query.get(SIGN_QUERY_PARAM)) is None:
            return False

        try:
            claims = jwt_wrapper.verify_and_decode(
                signature, secret, algorithms=["HS256"], options={"verify_iss": False}
            )
        except jwt.InvalidTokenError:
            return False

        if claims["path"] != request.path:
            return False

        params = [
            list(itm)  # claims stores tuples as lists
            for itm in request.query.items()
            if itm[0] not in SAFE_QUERY_PARAMS and itm[0] != SIGN_QUERY_PARAM
        ]
        if claims["params"] != params:
            return False

        refresh_token = hass.auth.async_get_refresh_token(claims["iss"])

        if refresh_token is None:
            return False

        request[KEY_HASS_USER] = refresh_token.user
        request[KEY_HASS_REFRESH_TOKEN_ID] = refresh_token.id
        return True

    supervisor_user_id: str | None = None

    async def async_authenticate_supervisor_unix_socket(request: Request) -> bool:
        """Authenticate a request from a Unix socket as the Supervisor user.

        The Unix Socket is dedicated and only available to Supervisor. To
        avoid the extra overhead and round trips for the authentication and
        refresh tokens, we directly authenticate requests from the socket as
        the Supervisor user.
        """
        nonlocal supervisor_user_id

        # Fast path: use cached user ID
        if supervisor_user_id is not None:
            if user := await hass.auth.async_get_user(supervisor_user_id):
                request[KEY_HASS_USER] = user
                return True
            supervisor_user_id = None

        # Slow path: find the Supervisor user by name
        for user in await hass.auth.async_get_users():
            if user.system_generated and user.name == HASSIO_USER_NAME:
                supervisor_user_id = user.id
                # Not setting KEY_HASS_REFRESH_TOKEN_ID since Supervisor user
                # doesn't use refresh tokens.
                request[KEY_HASS_USER] = user
                return True

        # The Unix socket should not be serving before the hassio integration
        # has created the Supervisor user. If we get here, something is wrong.
        _LOGGER.error(
            "Supervisor user not found; cannot authenticate Unix socket request"
        )
        raise HTTPInternalServerError

    @middleware
    async def auth_middleware(
        request: Request, handler: Callable[[Request], Awaitable[StreamResponse]]
    ) -> StreamResponse:
        """Authenticate as middleware."""
        authenticated = False

        if is_supervisor_unix_socket_request(request):
            authenticated = await async_authenticate_supervisor_unix_socket(request)
            auth_type = "supervisor unix socket"

        elif hdrs.AUTHORIZATION in request.headers and async_validate_auth_header(
            request
        ):
            authenticated = True
            auth_type = "bearer token"

        # We first start with a string check to avoid parsing query params
        # for every request.
        elif (
            request.method in ["GET", "HEAD"]
            and SIGN_QUERY_PARAM in request.query_string
            and async_validate_signed_request(request)
        ):
            authenticated = True
            auth_type = "signed request"

        if authenticated and _LOGGER.isEnabledFor(logging.DEBUG):
            _LOGGER.debug(
                "Authenticated %s for %s using %s",
                request.remote or "unknown remote",
                request.path,
                auth_type,
            )

        request[KEY_AUTHENTICATED] = authenticated
        return await handler(request)

    app.middlewares.append(auth_middleware)