auth.py

# -*- coding: utf-8 -*-
# Copyright 2014 - 2016 OpenMarket Ltd
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import logging
from typing import List, Optional, Tuple

import pymacaroons
from netaddr import IPAddress

from twisted.web.server import Request

import synapse.types
from synapse import event_auth
from synapse.api.auth_blocking import AuthBlocking
from synapse.api.constants import EventTypes, Membership
from synapse.api.errors import (
    AuthError,
    Codes,
    InvalidClientTokenError,
    MissingClientTokenError,
)
from synapse.api.room_versions import KNOWN_ROOM_VERSIONS
from synapse.events import EventBase
from synapse.logging import opentracing as opentracing
from synapse.types import StateMap, UserID
from synapse.util.caches import register_cache
from synapse.util.caches.lrucache import LruCache
from synapse.util.metrics import Measure

logger = logging.getLogger(__name__)


AuthEventTypes = (
    EventTypes.Create,
    EventTypes.Member,
    EventTypes.PowerLevels,
    EventTypes.JoinRules,
    EventTypes.RoomHistoryVisibility,
    EventTypes.ThirdPartyInvite,
)

# guests always get this device id.
GUEST_DEVICE_ID = "guest_device"


class _InvalidMacaroonException(Exception):
    pass


class Auth:
    """
    FIXME: This class contains a mix of functions for authenticating users
    of our client-server API and authenticating events added to room graphs.
    """

    def __init__(self, hs):
        self.hs = hs
        self.clock = hs.get_clock()
        self.store = hs.get_datastore()
        self.state = hs.get_state_handler()

        self.token_cache = LruCache(10000)
        register_cache("cache", "token_cache", self.token_cache)

        self._auth_blocking = AuthBlocking(self.hs)

        self._account_validity = hs.config.account_validity
        self._track_appservice_user_ips = hs.config.track_appservice_user_ips
        self._macaroon_secret_key = hs.config.macaroon_secret_key

    async def check_from_context(
        self, room_version: str, event, context, do_sig_check=True
    ):
        prev_state_ids = await context.get_prev_state_ids()
        auth_events_ids = self.compute_auth_events(
            event, prev_state_ids, for_verification=True
        )
        auth_events = await self.store.get_events(auth_events_ids)
        auth_events = {(e.type, e.state_key): e for e in auth_events.values()}

        room_version_obj = KNOWN_ROOM_VERSIONS[room_version]
        event_auth.check(
            room_version_obj, event, auth_events=auth_events, do_sig_check=do_sig_check
        )

    async def check_user_in_room(
        self,
        room_id: str,
        user_id: str,
        current_state: Optional[StateMap[EventBase]] = None,
        allow_departed_users: bool = False,
    ) -> EventBase:
        """Check if the user is in the room, or was at some point.
        Args:
            room_id: The room to check.

            user_id: The user to check.

            current_state: Optional map of the current state of the room.
                If provided then that map is used to check whether they are a
                member of the room. Otherwise the current membership is
                loaded from the database.

            allow_departed_users: if True, accept users that were previously
                members but have now departed.

        Raises:
            AuthError if the user is/was not in the room.
        Returns:
            Membership event for the user if the user was in the
            room. This will be the join event if they are currently joined to
            the room. This will be the leave event if they have left the room.
        """
        if current_state:
            member = current_state.get((EventTypes.Member, user_id), None)
        else:
            member = await self.state.get_current_state(
                room_id=room_id, event_type=EventTypes.Member, state_key=user_id
            )

        if member:
            membership = member.membership

            if membership == Membership.JOIN:
                return member

            # XXX this looks totally bogus. Why do we not allow users who have been banned,
            # or those who were members previously and have been re-invited?
            if allow_departed_users and membership == Membership.LEAVE:
                forgot = await self.store.did_forget(user_id, room_id)
                if not forgot:
                    return member

        raise AuthError(403, "User %s not in room %s" % (user_id, room_id))

    async def check_host_in_room(self, room_id, host):
        with Measure(self.clock, "check_host_in_room"):
            latest_event_ids = await self.store.is_host_joined(room_id, host)
            return latest_event_ids

    def can_federate(self, event, auth_events):
        creation_event = auth_events.get((EventTypes.Create, ""))

        return creation_event.content.get("m.federate", True) is True

    def get_public_keys(self, invite_event):
        return event_auth.get_public_keys(invite_event)

    async def get_user_by_req(
        self,
        request: Request,
        allow_guest: bool = False,
        rights: str = "access",
        allow_expired: bool = False,
    ) -> synapse.types.Requester:
        """ Get a registered user's ID.

        Args:
            request: An HTTP request with an access_token query parameter.
            allow_guest: If False, will raise an AuthError if the user making the
                request is a guest.
            rights: The operation being performed; the access token must allow this
            allow_expired: If True, allow the request through even if the account
                is expired, or session token lifetime has ended. Note that
                /login will deliver access tokens regardless of expiration.

        Returns:
            Resolves to the requester
        Raises:
            InvalidClientCredentialsError if no user by that token exists or the token
                is invalid.
            AuthError if access is denied for the user in the access token
        """
        try:
            ip_addr = self.hs.get_ip_from_request(request)
            user_agent = request.requestHeaders.getRawHeaders(
                b"User-Agent", default=[b""]
            )[0].decode("ascii", "surrogateescape")

            access_token = self.get_access_token_from_request(request)

            user_id, app_service = self._get_appservice_user_id(request)
            if user_id:
                request.authenticated_entity = user_id
                opentracing.set_tag("authenticated_entity", user_id)
                opentracing.set_tag("appservice_id", app_service.id)

                if ip_addr and self._track_appservice_user_ips:
                    await self.store.insert_client_ip(
                        user_id=user_id,
                        access_token=access_token,
                        ip=ip_addr,
                        user_agent=user_agent,
                        device_id="dummy-device",  # stubbed
                    )

                return synapse.types.create_requester(user_id, app_service=app_service)

            user_info = await self.get_user_by_access_token(
                access_token, rights, allow_expired=allow_expired
            )
            user = user_info["user"]
            token_id = user_info["token_id"]
            is_guest = user_info["is_guest"]
            shadow_banned = user_info["shadow_banned"]

            # Deny the request if the user account has expired.
            if self._account_validity.enabled and not allow_expired:
                user_id = user.to_string()
                if await self.store.is_account_expired(user_id, self.clock.time_msec()):
                    raise AuthError(
                        403, "User account has expired", errcode=Codes.EXPIRED_ACCOUNT
                    )

            # device_id may not be present if get_user_by_access_token has been
            # stubbed out.
            device_id = user_info.get("device_id")

            if user and access_token and ip_addr:
                await self.store.insert_client_ip(
                    user_id=user.to_string(),
                    access_token=access_token,
                    ip=ip_addr,
                    user_agent=user_agent,
                    device_id=device_id,
                )

            if is_guest and not allow_guest:
                raise AuthError(
                    403,
                    "Guest access not allowed",
                    errcode=Codes.GUEST_ACCESS_FORBIDDEN,
                )

            request.authenticated_entity = user.to_string()
            opentracing.set_tag("authenticated_entity", user.to_string())
            if device_id:
                opentracing.set_tag("device_id", device_id)

            return synapse.types.create_requester(
                user,
                token_id,
                is_guest,
                shadow_banned,
                device_id,
                app_service=app_service,
            )
        except KeyError:
            raise MissingClientTokenError()

    def _get_appservice_user_id(self, request):
        app_service = self.store.get_app_service_by_token(
            self.get_access_token_from_request(request)
        )

        if app_service is None:
            return None, None

        if app_service.ip_range_whitelist:
            ip_address = IPAddress(self.hs.get_ip_from_request(request))
            if ip_address not in app_service.ip_range_whitelist:
                return None, None

        if b"user_id" not in request.args:
            return app_service.sender, app_service

        user_id = request.args[b"user_id"][0].decode("utf8")
        if app_service.sender == user_id:
            return app_service.sender, app_service

        if not app_service.is_interested_in_user(user_id):
            raise AuthError(403, "Application service cannot masquerade as this user.")
        # Let ASes manipulate nonexistent users (e.g. to shadow-register them)
        # if not (yield self.store.get_user_by_id(user_id)):
        #     raise AuthError(
        #         403,
        #         "Application service has not registered this user"
        #     )
        return user_id, app_service

    async def get_user_by_access_token(
        self, token: str, rights: str = "access", allow_expired: bool = False,
    ) -> dict:
        """ Validate access token and get user_id from it

        Args:
            token: The access token to get the user by
            rights: The operation being performed; the access token must
                allow this
            allow_expired: If False, raises an InvalidClientTokenError
                if the token is expired
        Returns:
            dict that includes:
               `user` (UserID)
               `is_guest` (bool)
               `shadow_banned` (bool)
               `token_id` (int|None): access token id. May be None if guest
               `device_id` (str|None): device corresponding to access token
        Raises:
            InvalidClientTokenError if a user by that token exists, but the token is
                expired
            InvalidClientCredentialsError if no user by that token exists or the token
                is invalid
        """

        if rights == "access":
            # first look in the database
            r = await self._look_up_user_by_access_token(token)
            if r:
                valid_until_ms = r["valid_until_ms"]
                if (
                    not allow_expired
                    and valid_until_ms is not None
                    and valid_until_ms < self.clock.time_msec()
                ):
                    # there was a valid access token, but it has expired.
                    # soft-logout the user.
                    raise InvalidClientTokenError(
                        msg="Access token has expired", soft_logout=True
                    )

                return r

        # otherwise it needs to be a valid macaroon
        try:
            user_id, guest = self._parse_and_validate_macaroon(token, rights)
            user = UserID.from_string(user_id)

            if rights == "access":
                if not guest:
                    # non-guest access tokens must be in the database
                    logger.warning("Unrecognised access token - not in store.")
                    raise InvalidClientTokenError()

                # Guest access tokens are not stored in the database (there can
                # only be one access token per guest, anyway).
                #
                # In order to prevent guest access tokens being used as regular
                # user access tokens (and hence getting around the invalidation
                # process), we look up the user id and check that it is indeed
                # a guest user.
                #
                # It would of course be much easier to store guest access
                # tokens in the database as well, but that would break existing
                # guest tokens.
                stored_user = await self.store.get_user_by_id(user_id)
                if not stored_user:
                    raise InvalidClientTokenError("Unknown user_id %s" % user_id)
                if not stored_user["is_guest"]:
                    raise InvalidClientTokenError(
                        "Guest access token used for regular user"
                    )
                ret = {
                    "user": user,
                    "is_guest": True,
                    "shadow_banned": False,
                    "token_id": None,
                    # all guests get the same device id
                    "device_id": GUEST_DEVICE_ID,
                }
            elif rights == "delete_pusher":
                # We don't store these tokens in the database
                ret = {
                    "user": user,
                    "is_guest": False,
                    "shadow_banned": False,
                    "token_id": None,
                    "device_id": None,
                }
            else:
                raise RuntimeError("Unknown rights setting %s", rights)
            return ret
        except (
            _InvalidMacaroonException,
            pymacaroons.exceptions.MacaroonException,
            TypeError,
            ValueError,
        ) as e:
            logger.warning("Invalid macaroon in auth: %s %s", type(e), e)
            raise InvalidClientTokenError("Invalid macaroon passed.")

    def _parse_and_validate_macaroon(self, token, rights="access"):
        """Takes a macaroon and tries to parse and validate it. This is cached
        if and only if rights == access and there isn't an expiry.

        On invalid macaroon raises _InvalidMacaroonException

        Returns:
            (user_id, is_guest)
        """
        if rights == "access":
            cached = self.token_cache.get(token, None)
            if cached:
                return cached

        try:
            macaroon = pymacaroons.Macaroon.deserialize(token)
        except Exception:  # deserialize can throw more-or-less anything
            # doesn't look like a macaroon: treat it as an opaque token which
            # must be in the database.
            # TODO: it would be nice to get rid of this, but apparently some
            # people use access tokens which aren't macaroons
            raise _InvalidMacaroonException()

        try:
            user_id = self.get_user_id_from_macaroon(macaroon)

            guest = False
            for caveat in macaroon.caveats:
                if caveat.caveat_id == "guest = true":
                    guest = True

            self.validate_macaroon(macaroon, rights, user_id=user_id)
        except (pymacaroons.exceptions.MacaroonException, TypeError, ValueError):
            raise InvalidClientTokenError("Invalid macaroon passed.")

        if rights == "access":
            self.token_cache[token] = (user_id, guest)

        return user_id, guest

    def get_user_id_from_macaroon(self, macaroon):
        """Retrieve the user_id given by the caveats on the macaroon.

        Does *not* validate the macaroon.

        Args:
            macaroon (pymacaroons.Macaroon): The macaroon to validate

        Returns:
            (str) user id

        Raises:
            InvalidClientCredentialsError if there is no user_id caveat in the
                macaroon
        """
        user_prefix = "user_id = "
        for caveat in macaroon.caveats:
            if caveat.caveat_id.startswith(user_prefix):
                return caveat.caveat_id[len(user_prefix) :]
        raise InvalidClientTokenError("No user caveat in macaroon")

    def validate_macaroon(self, macaroon, type_string, user_id):
        """
        validate that a Macaroon is understood by and was signed by this server.

        Args:
            macaroon(pymacaroons.Macaroon): The macaroon to validate
            type_string(str): The kind of token required (e.g. "access",
                              "delete_pusher")
            user_id (str): The user_id required
        """
        v = pymacaroons.Verifier()

        # the verifier runs a test for every caveat on the macaroon, to check
        # that it is met for the current request. Each caveat must match at
        # least one of the predicates specified by satisfy_exact or
        # specify_general.
        v.satisfy_exact("gen = 1")
        v.satisfy_exact("type = " + type_string)
        v.satisfy_exact("user_id = %s" % user_id)
        v.satisfy_exact("guest = true")
        v.satisfy_general(self._verify_expiry)

        # access_tokens include a nonce for uniqueness: any value is acceptable
        v.satisfy_general(lambda c: c.startswith("nonce = "))

        v.verify(macaroon, self._macaroon_secret_key)

    def _verify_expiry(self, caveat):
        prefix = "time < "
        if not caveat.startswith(prefix):
            return False
        expiry = int(caveat[len(prefix) :])
        now = self.hs.get_clock().time_msec()
        return now < expiry

    async def _look_up_user_by_access_token(self, token):
        ret = await self.store.get_user_by_access_token(token)
        if not ret:
            return None

        # we use ret.get() below because *lots* of unit tests stub out
        # get_user_by_access_token in a way where it only returns a couple of
        # the fields.
        user_info = {
            "user": UserID.from_string(ret.get("name")),
            "token_id": ret.get("token_id", None),
            "is_guest": False,
            "shadow_banned": ret.get("shadow_banned"),
            "device_id": ret.get("device_id"),
            "valid_until_ms": ret.get("valid_until_ms"),
        }
        return user_info

    def get_appservice_by_req(self, request):
        token = self.get_access_token_from_request(request)
        service = self.store.get_app_service_by_token(token)
        if not service:
            logger.warning("Unrecognised appservice access token.")
            raise InvalidClientTokenError()
        request.authenticated_entity = service.sender
        return service

    async def is_server_admin(self, user: UserID) -> bool:
        """ Check if the given user is a local server admin.

        Args:
            user: user to check

        Returns:
            True if the user is an admin
        """
        return await self.store.is_server_admin(user)

    def compute_auth_events(
        self, event, current_state_ids: StateMap[str], for_verification: bool = False,
    ) -> List[str]:
        """Given an event and current state return the list of event IDs used
        to auth an event.

        If `for_verification` is False then only return auth events that
        should be added to the event's `auth_events`.

        Returns:
            List of event IDs.
        """

        if event.type == EventTypes.Create:
            return []

        # Currently we ignore the `for_verification` flag even though there are
        # some situations where we can drop particular auth events when adding
        # to the event's `auth_events` (e.g. joins pointing to previous joins
        # when room is publicly joinable). Dropping event IDs has the
        # advantage that the auth chain for the room grows slower, but we use
        # the auth chain in state resolution v2 to order events, which means
        # care must be taken if dropping events to ensure that it doesn't
        # introduce undesirable "state reset" behaviour.
        #
        # All of which sounds a bit tricky so we don't bother for now.

        auth_ids = []
        for etype, state_key in event_auth.auth_types_for_event(event):
            auth_ev_id = current_state_ids.get((etype, state_key))
            if auth_ev_id:
                auth_ids.append(auth_ev_id)

        return auth_ids

    async def check_can_change_room_list(self, room_id: str, user: UserID):
        """Determine whether the user is allowed to edit the room's entry in the
        published room list.

        Args:
            room_id
            user
        """

        is_admin = await self.is_server_admin(user)
        if is_admin:
            return True

        user_id = user.to_string()
        await self.check_user_in_room(room_id, user_id)

        # We currently require the user is a "moderator" in the room. We do this
        # by checking if they would (theoretically) be able to change the
        # m.room.canonical_alias events
        power_level_event = await self.state.get_current_state(
            room_id, EventTypes.PowerLevels, ""
        )

        auth_events = {}
        if power_level_event:
            auth_events[(EventTypes.PowerLevels, "")] = power_level_event

        send_level = event_auth.get_send_level(
            EventTypes.CanonicalAlias, "", power_level_event
        )
        user_level = event_auth.get_user_power_level(user_id, auth_events)

        return user_level >= send_level

    @staticmethod
    def has_access_token(request: Request):
        """Checks if the request has an access_token.

        Returns:
            bool: False if no access_token was given, True otherwise.
        """
        query_params = request.args.get(b"access_token")
        auth_headers = request.requestHeaders.getRawHeaders(b"Authorization")
        return bool(query_params) or bool(auth_headers)

    @staticmethod
    def get_access_token_from_request(request: Request):
        """Extracts the access_token from the request.

        Args:
            request: The http request.
        Returns:
            unicode: The access_token
        Raises:
            MissingClientTokenError: If there isn't a single access_token in the
                request
        """

        auth_headers = request.requestHeaders.getRawHeaders(b"Authorization")
        query_params = request.args.get(b"access_token")
        if auth_headers:
            # Try the get the access_token from a "Authorization: Bearer"
            # header
            if query_params is not None:
                raise MissingClientTokenError(
                    "Mixing Authorization headers and access_token query parameters."
                )
            if len(auth_headers) > 1:
                raise MissingClientTokenError("Too many Authorization headers.")
            parts = auth_headers[0].split(b" ")
            if parts[0] == b"Bearer" and len(parts) == 2:
                return parts[1].decode("ascii")
            else:
                raise MissingClientTokenError("Invalid Authorization header.")
        else:
            # Try to get the access_token from the query params.
            if not query_params:
                raise MissingClientTokenError()

            return query_params[0].decode("ascii")

    async def check_user_in_room_or_world_readable(
        self, room_id: str, user_id: str, allow_departed_users: bool = False
    ) -> Tuple[str, Optional[str]]:
        """Checks that the user is or was in the room or the room is world
        readable. If it isn't then an exception is raised.

        Args:
            room_id: room to check
            user_id: user to check
            allow_departed_users: if True, accept users that were previously
                members but have now departed

        Returns:
            Resolves to the current membership of the user in the room and the
            membership event ID of the user. If the user is not in the room and
            never has been, then `(Membership.JOIN, None)` is returned.
        """

        try:
            # check_user_in_room will return the most recent membership
            # event for the user if:
            #  * The user is a non-guest user, and was ever in the room
            #  * The user is a guest user, and has joined the room
            # else it will throw.
            member_event = await self.check_user_in_room(
                room_id, user_id, allow_departed_users=allow_departed_users
            )
            return member_event.membership, member_event.event_id
        except AuthError:
            visibility = await self.state.get_current_state(
                room_id, EventTypes.RoomHistoryVisibility, ""
            )
            if (
                visibility
                and visibility.content["history_visibility"] == "world_readable"
            ):
                return Membership.JOIN, None
            raise AuthError(
                403,
                "User %s not in room %s, and room previews are disabled"
                % (user_id, room_id),
            )

    def check_auth_blocking(self, *args, **kwargs):
        return self._auth_blocking.check_auth_blocking(*args, **kwargs)