synapse-product/synapse/handlers/auth.py

# -*- coding: utf-8 -*-
# Copyright 2014 - 2016 OpenMarket Ltd
# Copyright 2017 Vector Creations 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.
from twisted.internet import defer

from ._base import BaseHandler
from synapse.api.constants import LoginType
from synapse.api.errors import (
    AuthError, Codes, InteractiveAuthIncompleteError, LoginError, StoreError,
    SynapseError,
)
from synapse.module_api import ModuleApi
from synapse.types import UserID
from synapse.util.async import run_on_reactor
from synapse.util.caches.expiringcache import ExpiringCache

from twisted.web.client import PartialDownloadError

import logging
import bcrypt
import pymacaroons
import simplejson

import synapse.util.stringutils as stringutils


logger = logging.getLogger(__name__)


class AuthHandler(BaseHandler):
    SESSION_EXPIRE_MS = 48 * 60 * 60 * 1000

    def __init__(self, hs):
        """
        Args:
            hs (synapse.server.HomeServer):
        """
        super(AuthHandler, self).__init__(hs)
        self.checkers = {
            LoginType.PASSWORD: self._check_password_auth,
            LoginType.RECAPTCHA: self._check_recaptcha,
            LoginType.EMAIL_IDENTITY: self._check_email_identity,
            LoginType.MSISDN: self._check_msisdn,
            LoginType.DUMMY: self._check_dummy_auth,
        }
        self.bcrypt_rounds = hs.config.bcrypt_rounds

        # This is not a cache per se, but a store of all current sessions that
        # expire after N hours
        self.sessions = ExpiringCache(
            cache_name="register_sessions",
            clock=hs.get_clock(),
            expiry_ms=self.SESSION_EXPIRE_MS,
            reset_expiry_on_get=True,
        )

        account_handler = ModuleApi(hs, self)
        self.password_providers = [
            module(config=config, account_handler=account_handler)
            for module, config in hs.config.password_providers
        ]

        logger.info("Extra password_providers: %r", self.password_providers)

        self.hs = hs  # FIXME better possibility to access registrationHandler later?
        self.macaroon_gen = hs.get_macaroon_generator()
        self._password_enabled = hs.config.password_enabled

        login_types = set()
        if self._password_enabled:
            login_types.add(LoginType.PASSWORD)
        for provider in self.password_providers:
            if hasattr(provider, "get_supported_login_types"):
                login_types.update(
                    provider.get_supported_login_types().keys()
                )
        self._supported_login_types = frozenset(login_types)

    @defer.inlineCallbacks
    def check_auth(self, flows, clientdict, clientip):
        """
        Takes a dictionary sent by the client in the login / registration
        protocol and handles the User-Interactive Auth flow.

        As a side effect, this function fills in the 'creds' key on the user's
        session with a map, which maps each auth-type (str) to the relevant
        identity authenticated by that auth-type (mostly str, but for captcha, bool).

        If no auth flows have been completed successfully, raises an
        InteractiveAuthIncompleteError. To handle this, you can use
        synapse.rest.client.v2_alpha._base.interactive_auth_handler as a
        decorator.

        Args:
            flows (list): A list of login flows. Each flow is an ordered list of
                          strings representing auth-types. At least one full
                          flow must be completed in order for auth to be successful.

            clientdict: The dictionary from the client root level, not the
                        'auth' key: this method prompts for auth if none is sent.

            clientip (str): The IP address of the client.

        Returns:
            defer.Deferred[dict, dict, str]: a deferred tuple of
                (creds, params, session_id).

                'creds' contains the authenticated credentials of each stage.

                'params' contains the parameters for this request (which may
                have been given only in a previous call).

                'session_id' is the ID of this session, either passed in by the
                client or assigned by this call

        Raises:
            InteractiveAuthIncompleteError if the client has not yet completed
                all the stages in any of the permitted flows.
        """

        authdict = None
        sid = None
        if clientdict and 'auth' in clientdict:
            authdict = clientdict['auth']
            del clientdict['auth']
            if 'session' in authdict:
                sid = authdict['session']
        session = self._get_session_info(sid)

        if len(clientdict) > 0:
            # This was designed to allow the client to omit the parameters
            # and just supply the session in subsequent calls so it split
            # auth between devices by just sharing the session, (eg. so you
            # could continue registration from your phone having clicked the
            # email auth link on there). It's probably too open to abuse
            # because it lets unauthenticated clients store arbitrary objects
            # on a home server.
            # Revisit: Assumimg the REST APIs do sensible validation, the data
            # isn't arbintrary.
            session['clientdict'] = clientdict
            self._save_session(session)
        elif 'clientdict' in session:
            clientdict = session['clientdict']

        if not authdict:
            raise InteractiveAuthIncompleteError(
                self._auth_dict_for_flows(flows, session),
            )

        if 'creds' not in session:
            session['creds'] = {}
        creds = session['creds']

        # check auth type currently being presented
        errordict = {}
        if 'type' in authdict:
            login_type = authdict['type']
            if login_type not in self.checkers:
                raise LoginError(400, "", Codes.UNRECOGNIZED)
            try:
                result = yield self.checkers[login_type](authdict, clientip)
                if result:
                    creds[login_type] = result
                    self._save_session(session)
            except LoginError, e:
                if login_type == LoginType.EMAIL_IDENTITY:
                    # riot used to have a bug where it would request a new
                    # validation token (thus sending a new email) each time it
                    # got a 401 with a 'flows' field.
                    # (https://github.com/vector-im/vector-web/issues/2447).
                    #
                    # Grandfather in the old behaviour for now to avoid
                    # breaking old riot deployments.
                    raise e

                # this step failed. Merge the error dict into the response
                # so that the client can have another go.
                errordict = e.error_dict()

        for f in flows:
            if len(set(f) - set(creds.keys())) == 0:
                # it's very useful to know what args are stored, but this can
                # include the password in the case of registering, so only log
                # the keys (confusingly, clientdict may contain a password
                # param, creds is just what the user authed as for UI auth
                # and is not sensitive).
                logger.info(
                    "Auth completed with creds: %r. Client dict has keys: %r",
                    creds, clientdict.keys()
                )
                defer.returnValue((creds, clientdict, session['id']))

        ret = self._auth_dict_for_flows(flows, session)
        ret['completed'] = creds.keys()
        ret.update(errordict)
        raise InteractiveAuthIncompleteError(
            ret,
        )

    @defer.inlineCallbacks
    def add_oob_auth(self, stagetype, authdict, clientip):
        """
        Adds the result of out-of-band authentication into an existing auth
        session. Currently used for adding the result of fallback auth.
        """
        if stagetype not in self.checkers:
            raise LoginError(400, "", Codes.MISSING_PARAM)
        if 'session' not in authdict:
            raise LoginError(400, "", Codes.MISSING_PARAM)

        sess = self._get_session_info(
            authdict['session']
        )
        if 'creds' not in sess:
            sess['creds'] = {}
        creds = sess['creds']

        result = yield self.checkers[stagetype](authdict, clientip)
        if result:
            creds[stagetype] = result
            self._save_session(sess)
            defer.returnValue(True)
        defer.returnValue(False)

    def get_session_id(self, clientdict):
        """
        Gets the session ID for a client given the client dictionary

        Args:
            clientdict: The dictionary sent by the client in the request

        Returns:
            str|None: The string session ID the client sent. If the client did
                not send a session ID, returns None.
        """
        sid = None
        if clientdict and 'auth' in clientdict:
            authdict = clientdict['auth']
            if 'session' in authdict:
                sid = authdict['session']
        return sid

    def set_session_data(self, session_id, key, value):
        """
        Store a key-value pair into the sessions data associated with this
        request. This data is stored server-side and cannot be modified by
        the client.

        Args:
            session_id (string): The ID of this session as returned from check_auth
            key (string): The key to store the data under
            value (any): The data to store
        """
        sess = self._get_session_info(session_id)
        sess.setdefault('serverdict', {})[key] = value
        self._save_session(sess)

    def get_session_data(self, session_id, key, default=None):
        """
        Retrieve data stored with set_session_data

        Args:
            session_id (string): The ID of this session as returned from check_auth
            key (string): The key to store the data under
            default (any): Value to return if the key has not been set
        """
        sess = self._get_session_info(session_id)
        return sess.setdefault('serverdict', {}).get(key, default)

    @defer.inlineCallbacks
    def _check_password_auth(self, authdict, _):
        if "user" not in authdict or "password" not in authdict:
            raise LoginError(400, "", Codes.MISSING_PARAM)

        user_id = authdict["user"]
        password = authdict["password"]

        (canonical_id, callback) = yield self.validate_login(user_id, {
            "type": LoginType.PASSWORD,
            "password": password,
        })
        defer.returnValue(canonical_id)

    @defer.inlineCallbacks
    def _check_recaptcha(self, authdict, clientip):
        try:
            user_response = authdict["response"]
        except KeyError:
            # Client tried to provide captcha but didn't give the parameter:
            # bad request.
            raise LoginError(
                400, "Captcha response is required",
                errcode=Codes.CAPTCHA_NEEDED
            )

        logger.info(
            "Submitting recaptcha response %s with remoteip %s",
            user_response, clientip
        )

        # TODO: get this from the homeserver rather than creating a new one for
        # each request
        try:
            client = self.hs.get_simple_http_client()
            resp_body = yield client.post_urlencoded_get_json(
                self.hs.config.recaptcha_siteverify_api,
                args={
                    'secret': self.hs.config.recaptcha_private_key,
                    'response': user_response,
                    'remoteip': clientip,
                }
            )
        except PartialDownloadError as pde:
            # Twisted is silly
            data = pde.response
            resp_body = simplejson.loads(data)

        if 'success' in resp_body:
            # Note that we do NOT check the hostname here: we explicitly
            # intend the CAPTCHA to be presented by whatever client the
            # user is using, we just care that they have completed a CAPTCHA.
            logger.info(
                "%s reCAPTCHA from hostname %s",
                "Successful" if resp_body['success'] else "Failed",
                resp_body.get('hostname')
            )
            if resp_body['success']:
                defer.returnValue(True)
        raise LoginError(401, "", errcode=Codes.UNAUTHORIZED)

    def _check_email_identity(self, authdict, _):
        return self._check_threepid('email', authdict)

    def _check_msisdn(self, authdict, _):
        return self._check_threepid('msisdn', authdict)

    @defer.inlineCallbacks
    def _check_dummy_auth(self, authdict, _):
        yield run_on_reactor()
        defer.returnValue(True)

    @defer.inlineCallbacks
    def _check_threepid(self, medium, authdict):
        yield run_on_reactor()

        if 'threepid_creds' not in authdict:
            raise LoginError(400, "Missing threepid_creds", Codes.MISSING_PARAM)

        threepid_creds = authdict['threepid_creds']

        identity_handler = self.hs.get_handlers().identity_handler

        logger.info("Getting validated threepid. threepidcreds: %r", (threepid_creds,))
        threepid = yield identity_handler.threepid_from_creds(threepid_creds)

        if not threepid:
            raise LoginError(401, "", errcode=Codes.UNAUTHORIZED)

        if threepid['medium'] != medium:
            raise LoginError(
                401,
                "Expecting threepid of type '%s', got '%s'" % (
                    medium, threepid['medium'],
                ),
                errcode=Codes.UNAUTHORIZED
            )

        threepid['threepid_creds'] = authdict['threepid_creds']

        defer.returnValue(threepid)

    def _get_params_recaptcha(self):
        return {"public_key": self.hs.config.recaptcha_public_key}

    def _auth_dict_for_flows(self, flows, session):
        public_flows = []
        for f in flows:
            public_flows.append(f)

        get_params = {
            LoginType.RECAPTCHA: self._get_params_recaptcha,
        }

        params = {}

        for f in public_flows:
            for stage in f:
                if stage in get_params and stage not in params:
                    params[stage] = get_params[stage]()

        return {
            "session": session['id'],
            "flows": [{"stages": f} for f in public_flows],
            "params": params
        }

    def _get_session_info(self, session_id):
        if session_id not in self.sessions:
            session_id = None

        if not session_id:
            # create a new session
            while session_id is None or session_id in self.sessions:
                session_id = stringutils.random_string(24)
            self.sessions[session_id] = {
                "id": session_id,
            }

        return self.sessions[session_id]

    @defer.inlineCallbacks
    def get_access_token_for_user_id(self, user_id, device_id=None):
        """
        Creates a new access token for the user with the given user ID.

        The user is assumed to have been authenticated by some other
        machanism (e.g. CAS), and the user_id converted to the canonical case.

        The device will be recorded in the table if it is not there already.

        Args:
            user_id (str): canonical User ID
            device_id (str|None): the device ID to associate with the tokens.
               None to leave the tokens unassociated with a device (deprecated:
               we should always have a device ID)
        Returns:
              The access token for the user's session.
        Raises:
            StoreError if there was a problem storing the token.
        """
        logger.info("Logging in user %s on device %s", user_id, device_id)
        access_token = yield self.issue_access_token(user_id, device_id)

        # the device *should* have been registered before we got here; however,
        # it's possible we raced against a DELETE operation. The thing we
        # really don't want is active access_tokens without a record of the
        # device, so we double-check it here.
        if device_id is not None:
            try:
                yield self.store.get_device(user_id, device_id)
            except StoreError:
                yield self.store.delete_access_token(access_token)
                raise StoreError(400, "Login raced against device deletion")

        defer.returnValue(access_token)

    @defer.inlineCallbacks
    def check_user_exists(self, user_id):
        """
        Checks to see if a user with the given id exists. Will check case
        insensitively, but return None if there are multiple inexact matches.

        Args:
            (str) user_id: complete @user:id

        Returns:
            defer.Deferred: (str) canonical_user_id, or None if zero or
            multiple matches
        """
        res = yield self._find_user_id_and_pwd_hash(user_id)
        if res is not None:
            defer.returnValue(res[0])
        defer.returnValue(None)

    @defer.inlineCallbacks
    def _find_user_id_and_pwd_hash(self, user_id):
        """Checks to see if a user with the given id exists. Will check case
        insensitively, but will return None if there are multiple inexact
        matches.

        Returns:
            tuple: A 2-tuple of `(canonical_user_id, password_hash)`
            None: if there is not exactly one match
        """
        user_infos = yield self.store.get_users_by_id_case_insensitive(user_id)

        result = None
        if not user_infos:
            logger.warn("Attempted to login as %s but they do not exist", user_id)
        elif len(user_infos) == 1:
            # a single match (possibly not exact)
            result = user_infos.popitem()
        elif user_id in user_infos:
            # multiple matches, but one is exact
            result = (user_id, user_infos[user_id])
        else:
            # multiple matches, none of them exact
            logger.warn(
                "Attempted to login as %s but it matches more than one user "
                "inexactly: %r",
                user_id, user_infos.keys()
            )
        defer.returnValue(result)

    def get_supported_login_types(self):
        """Get a the login types supported for the /login API

        By default this is just 'm.login.password' (unless password_enabled is
        False in the config file), but password auth providers can provide
        other login types.

        Returns:
            Iterable[str]: login types
        """
        return self._supported_login_types

    @defer.inlineCallbacks
    def validate_login(self, username, login_submission):
        """Authenticates the user for the /login API

        Also used by the user-interactive auth flow to validate
        m.login.password auth types.

        Args:
            username (str): username supplied by the user
            login_submission (dict): the whole of the login submission
                (including 'type' and other relevant fields)
        Returns:
            Deferred[str, func]: canonical user id, and optional callback
                to be called once the access token and device id are issued
        Raises:
            StoreError if there was a problem accessing the database
            SynapseError if there was a problem with the request
            LoginError if there was an authentication problem.
        """

        if username.startswith('@'):
            qualified_user_id = username
        else:
            qualified_user_id = UserID(
                username, self.hs.hostname
            ).to_string()

        login_type = login_submission.get("type")
        known_login_type = False

        # special case to check for "password" for the check_password interface
        # for the auth providers
        password = login_submission.get("password")
        if login_type == LoginType.PASSWORD:
            if not self._password_enabled:
                raise SynapseError(400, "Password login has been disabled.")
            if not password:
                raise SynapseError(400, "Missing parameter: password")

        for provider in self.password_providers:
            if (hasattr(provider, "check_password")
                    and login_type == LoginType.PASSWORD):
                known_login_type = True
                is_valid = yield provider.check_password(
                    qualified_user_id, password,
                )
                if is_valid:
                    defer.returnValue((qualified_user_id, None))

            if (not hasattr(provider, "get_supported_login_types")
                    or not hasattr(provider, "check_auth")):
                # this password provider doesn't understand custom login types
                continue

            supported_login_types = provider.get_supported_login_types()
            if login_type not in supported_login_types:
                # this password provider doesn't understand this login type
                continue

            known_login_type = True
            login_fields = supported_login_types[login_type]

            missing_fields = []
            login_dict = {}
            for f in login_fields:
                if f not in login_submission:
                    missing_fields.append(f)
                else:
                    login_dict[f] = login_submission[f]
            if missing_fields:
                raise SynapseError(
                    400, "Missing parameters for login type %s: %s" % (
                        login_type,
                        missing_fields,
                    ),
                )

            result = yield provider.check_auth(
                username, login_type, login_dict,
            )
            if result:
                if isinstance(result, str):
                    result = (result, None)
                defer.returnValue(result)

        if login_type == LoginType.PASSWORD:
            known_login_type = True

            canonical_user_id = yield self._check_local_password(
                qualified_user_id, password,
            )

            if canonical_user_id:
                defer.returnValue((canonical_user_id, None))

        if not known_login_type:
            raise SynapseError(400, "Unknown login type %s" % login_type)

        # unknown username or invalid password. We raise a 403 here, but note
        # that if we're doing user-interactive login, it turns all LoginErrors
        # into a 401 anyway.
        raise LoginError(
            403, "Invalid password",
            errcode=Codes.FORBIDDEN
        )

    @defer.inlineCallbacks
    def _check_local_password(self, user_id, password):
        """Authenticate a user against the local password database.

        user_id is checked case insensitively, but will return None if there are
        multiple inexact matches.

        Args:
            user_id (str): complete @user:id
        Returns:
            (str) the canonical_user_id, or None if unknown user / bad password
        """
        lookupres = yield self._find_user_id_and_pwd_hash(user_id)
        if not lookupres:
            defer.returnValue(None)
        (user_id, password_hash) = lookupres
        result = self.validate_hash(password, password_hash)
        if not result:
            logger.warn("Failed password login for user %s", user_id)
            defer.returnValue(None)
        defer.returnValue(user_id)

    @defer.inlineCallbacks
    def issue_access_token(self, user_id, device_id=None):
        access_token = self.macaroon_gen.generate_access_token(user_id)
        yield self.store.add_access_token_to_user(user_id, access_token,
                                                  device_id)
        defer.returnValue(access_token)

    def validate_short_term_login_token_and_get_user_id(self, login_token):
        auth_api = self.hs.get_auth()
        try:
            macaroon = pymacaroons.Macaroon.deserialize(login_token)
            user_id = auth_api.get_user_id_from_macaroon(macaroon)
            auth_api.validate_macaroon(macaroon, "login", True, user_id)
            return user_id
        except Exception:
            raise AuthError(403, "Invalid token", errcode=Codes.FORBIDDEN)

    @defer.inlineCallbacks
    def delete_access_token(self, access_token):
        """Invalidate a single access token

        Args:
            access_token (str): access token to be deleted

        Returns:
            Deferred
        """
        user_info = yield self.auth.get_user_by_access_token(access_token)
        yield self.store.delete_access_token(access_token)

        # see if any of our auth providers want to know about this
        for provider in self.password_providers:
            if hasattr(provider, "on_logged_out"):
                yield provider.on_logged_out(
                    user_id=str(user_info["user"]),
                    device_id=user_info["device_id"],
                    access_token=access_token,
                )

        # delete pushers associated with this access token
        if user_info["token_id"] is not None:
            yield self.hs.get_pusherpool().remove_pushers_by_access_token(
                str(user_info["user"]), (user_info["token_id"], )
            )

    @defer.inlineCallbacks
    def delete_access_tokens_for_user(self, user_id, except_token_id=None,
                                      device_id=None):
        """Invalidate access tokens belonging to a user

        Args:
            user_id (str):  ID of user the tokens belong to
            except_token_id (str|None): access_token ID which should *not* be
                deleted
            device_id (str|None):  ID of device the tokens are associated with.
                If None, tokens associated with any device (or no device) will
                be deleted
        Returns:
            Deferred
        """
        tokens_and_devices = yield self.store.user_delete_access_tokens(
            user_id, except_token_id=except_token_id, device_id=device_id,
        )

        # see if any of our auth providers want to know about this
        for provider in self.password_providers:
            if hasattr(provider, "on_logged_out"):
                for token, token_id, device_id in tokens_and_devices:
                    yield provider.on_logged_out(
                        user_id=user_id,
                        device_id=device_id,
                        access_token=token,
                    )

        # delete pushers associated with the access tokens
        yield self.hs.get_pusherpool().remove_pushers_by_access_token(
            user_id, (token_id for _, token_id, _ in tokens_and_devices),
        )

    @defer.inlineCallbacks
    def add_threepid(self, user_id, medium, address, validated_at):
        # 'Canonicalise' email addresses down to lower case.
        # We've now moving towards the Home Server being the entity that
        # is responsible for validating threepids used for resetting passwords
        # on accounts, so in future Synapse will gain knowledge of specific
        # types (mediums) of threepid. For now, we still use the existing
        # infrastructure, but this is the start of synapse gaining knowledge
        # of specific types of threepid (and fixes the fact that checking
        # for the presence of an email address during password reset was
        # case sensitive).
        if medium == 'email':
            address = address.lower()

        yield self.store.user_add_threepid(
            user_id, medium, address, validated_at,
            self.hs.get_clock().time_msec()
        )

    @defer.inlineCallbacks
    def delete_threepid(self, user_id, medium, address):
        # 'Canonicalise' email addresses as per above
        if medium == 'email':
            address = address.lower()

        ret = yield self.store.user_delete_threepid(
            user_id, medium, address,
        )
        defer.returnValue(ret)

    def _save_session(self, session):
        # TODO: Persistent storage
        logger.debug("Saving session %s", session)
        session["last_used"] = self.hs.get_clock().time_msec()
        self.sessions[session["id"]] = session

    def hash(self, password):
        """Computes a secure hash of password.

        Args:
            password (str): Password to hash.

        Returns:
            Hashed password (str).
        """
        return bcrypt.hashpw(password.encode('utf8') + self.hs.config.password_pepper,
                             bcrypt.gensalt(self.bcrypt_rounds))

    def validate_hash(self, password, stored_hash):
        """Validates that self.hash(password) == stored_hash.

        Args:
            password (str): Password to hash.
            stored_hash (str): Expected hash value.

        Returns:
            Whether self.hash(password) == stored_hash (bool).
        """
        if stored_hash:
            return bcrypt.hashpw(password.encode('utf8') + self.hs.config.password_pepper,
                                 stored_hash.encode('utf8')) == stored_hash
        else:
            return False


class MacaroonGeneartor(object):
    def __init__(self, hs):
        self.clock = hs.get_clock()
        self.server_name = hs.config.server_name
        self.macaroon_secret_key = hs.config.macaroon_secret_key

    def generate_access_token(self, user_id, extra_caveats=None):
        extra_caveats = extra_caveats or []
        macaroon = self._generate_base_macaroon(user_id)
        macaroon.add_first_party_caveat("type = access")
        # Include a nonce, to make sure that each login gets a different
        # access token.
        macaroon.add_first_party_caveat("nonce = %s" % (
            stringutils.random_string_with_symbols(16),
        ))
        for caveat in extra_caveats:
            macaroon.add_first_party_caveat(caveat)
        return macaroon.serialize()

    def generate_short_term_login_token(self, user_id, duration_in_ms=(2 * 60 * 1000)):
        macaroon = self._generate_base_macaroon(user_id)
        macaroon.add_first_party_caveat("type = login")
        now = self.clock.time_msec()
        expiry = now + duration_in_ms
        macaroon.add_first_party_caveat("time < %d" % (expiry,))
        return macaroon.serialize()

    def generate_delete_pusher_token(self, user_id):
        macaroon = self._generate_base_macaroon(user_id)
        macaroon.add_first_party_caveat("type = delete_pusher")
        return macaroon.serialize()

    def _generate_base_macaroon(self, user_id):
        macaroon = pymacaroons.Macaroon(
            location=self.server_name,
            identifier="key",
            key=self.macaroon_secret_key)
        macaroon.add_first_party_caveat("gen = 1")
        macaroon.add_first_party_caveat("user_id = %s" % (user_id,))
        return macaroon