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.

import logging
import time
import unicodedata
import urllib.parse
from typing import Any, Callable, Dict, Iterable, List, Optional, Tuple, Union

import attr
import bcrypt  # type: ignore[import]
import pymacaroons

import synapse.util.stringutils as stringutils
from synapse.api.constants import LoginType
from synapse.api.errors import (
    AuthError,
    Codes,
    InteractiveAuthIncompleteError,
    LoginError,
    StoreError,
    SynapseError,
    UserDeactivatedError,
)
from synapse.api.ratelimiting import Ratelimiter
from synapse.handlers.ui_auth import INTERACTIVE_AUTH_CHECKERS
from synapse.handlers.ui_auth.checkers import UserInteractiveAuthChecker
from synapse.http.server import finish_request
from synapse.http.site import SynapseRequest
from synapse.logging.context import defer_to_thread
from synapse.metrics.background_process_metrics import run_as_background_process
from synapse.module_api import ModuleApi
from synapse.push.mailer import load_jinja2_templates
from synapse.types import Requester, UserID

from ._base import BaseHandler

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 = {}  # type: Dict[str, UserInteractiveAuthChecker]
        for auth_checker_class in INTERACTIVE_AUTH_CHECKERS:
            inst = auth_checker_class(hs)
            if inst.is_enabled():
                self.checkers[inst.AUTH_TYPE] = inst  # type: ignore

        self.bcrypt_rounds = hs.config.bcrypt_rounds

        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
        self._sso_enabled = hs.config.saml2_enabled or hs.config.cas_enabled

        # we keep this as a list despite the O(N^2) implication so that we can
        # keep PASSWORD first and avoid confusing clients which pick the first
        # type in the list. (NB that the spec doesn't require us to do so and
        # clients which favour types that they don't understand over those that
        # they do are technically broken)
        login_types = []
        if self._password_enabled:
            login_types.append(LoginType.PASSWORD)
        for provider in self.password_providers:
            if hasattr(provider, "get_supported_login_types"):
                for t in provider.get_supported_login_types().keys():
                    if t not in login_types:
                        login_types.append(t)
        self._supported_login_types = login_types
        # Login types and UI Auth types have a heavy overlap, but are not
        # necessarily identical. Login types have SSO (and other login types)
        # added in the rest layer, see synapse.rest.client.v1.login.LoginRestServerlet.on_GET.
        ui_auth_types = login_types.copy()
        if self._sso_enabled:
            ui_auth_types.append(LoginType.SSO)
        self._supported_ui_auth_types = ui_auth_types

        # Ratelimiter for failed auth during UIA. Uses same ratelimit config
        # as per `rc_login.failed_attempts`.
        self._failed_uia_attempts_ratelimiter = Ratelimiter()

        self._clock = self.hs.get_clock()

        # Expire old UI auth sessions after a period of time.
        if hs.config.worker_app is None:
            self._clock.looping_call(
                run_as_background_process,
                5 * 60 * 1000,
                "expire_old_sessions",
                self._expire_old_sessions,
            )

        # Load the SSO HTML templates.

        # The following template is shown to the user during a client login via SSO,
        # after the SSO completes and before redirecting them back to their client.
        # It notifies the user they are about to give access to their matrix account
        # to the client.
        self._sso_redirect_confirm_template = load_jinja2_templates(
            hs.config.sso_redirect_confirm_template_dir, ["sso_redirect_confirm.html"],
        )[0]
        # The following template is shown during user interactive authentication
        # in the fallback auth scenario. It notifies the user that they are
        # authenticating for an operation to occur on their account.
        self._sso_auth_confirm_template = load_jinja2_templates(
            hs.config.sso_redirect_confirm_template_dir, ["sso_auth_confirm.html"],
        )[0]
        # The following template is shown after a successful user interactive
        # authentication session. It tells the user they can close the window.
        self._sso_auth_success_template = hs.config.sso_auth_success_template
        # The following template is shown during the SSO authentication process if
        # the account is deactivated.
        self._sso_account_deactivated_template = (
            hs.config.sso_account_deactivated_template
        )

        self._server_name = hs.config.server_name

        # cast to tuple for use with str.startswith
        self._whitelisted_sso_clients = tuple(hs.config.sso_client_whitelist)

    async def validate_user_via_ui_auth(
        self,
        requester: Requester,
        request: SynapseRequest,
        request_body: Dict[str, Any],
        clientip: str,
        description: str,
    ) -> dict:
        """
        Checks that the user is who they claim to be, via a UI auth.

        This is used for things like device deletion and password reset where
        the user already has a valid access token, but we want to double-check
        that it isn't stolen by re-authenticating them.

        Args:
            requester: The user, as given by the access token

            request: The request sent by the client.

            request_body: The body of the request sent by the client

            clientip: The IP address of the client.

            description: A human readable string to be displayed to the user that
                         describes the operation happening on their account.

        Returns:
            The parameters for this request (which may
                have been given only in a previous call).

        Raises:
            InteractiveAuthIncompleteError if the client has not yet completed
                any of the permitted login flows

            AuthError if the client has completed a login flow, and it gives
                a different user to `requester`

            LimitExceededError if the ratelimiter's failed request count for this
                user is too high to proceed

        """

        user_id = requester.user.to_string()

        # Check if we should be ratelimited due to too many previous failed attempts
        self._failed_uia_attempts_ratelimiter.ratelimit(
            user_id,
            time_now_s=self._clock.time(),
            rate_hz=self.hs.config.rc_login_failed_attempts.per_second,
            burst_count=self.hs.config.rc_login_failed_attempts.burst_count,
            update=False,
        )

        # build a list of supported flows
        flows = [[login_type] for login_type in self._supported_ui_auth_types]

        try:
            result, params, _ = await self.check_auth(
                flows, request, request_body, clientip, description
            )
        except LoginError:
            # Update the ratelimite to say we failed (`can_do_action` doesn't raise).
            self._failed_uia_attempts_ratelimiter.can_do_action(
                user_id,
                time_now_s=self._clock.time(),
                rate_hz=self.hs.config.rc_login_failed_attempts.per_second,
                burst_count=self.hs.config.rc_login_failed_attempts.burst_count,
                update=True,
            )
            raise

        # find the completed login type
        for login_type in self._supported_ui_auth_types:
            if login_type not in result:
                continue

            user_id = result[login_type]
            break
        else:
            # this can't happen
            raise Exception("check_auth returned True but no successful login type")

        # check that the UI auth matched the access token
        if user_id != requester.user.to_string():
            raise AuthError(403, "Invalid auth")

        return params

    def get_enabled_auth_types(self):
        """Return the enabled user-interactive authentication types

        Returns the UI-Auth types which are supported by the homeserver's current
        config.
        """
        return self.checkers.keys()

    async def check_auth(
        self,
        flows: List[List[str]],
        request: SynapseRequest,
        clientdict: Dict[str, Any],
        clientip: str,
        description: str,
    ) -> Tuple[dict, dict, str]:
        """
        Takes a dictionary sent by the client in the login / registration
        protocol and handles the User-Interactive Auth flow.

        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: 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.

            request: The request sent by the client.

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

            clientip: The IP address of the client.

            description: A human readable string to be displayed to the user that
                         describes the operation happening on their account.

        Returns:
            A 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  # type: Optional[str]
        if clientdict and "auth" in clientdict:
            authdict = clientdict["auth"]
            del clientdict["auth"]
            if "session" in authdict:
                sid = authdict["session"]

        # Convert the URI and method to strings.
        uri = request.uri.decode("utf-8")
        method = request.uri.decode("utf-8")

        # If there's no session ID, create a new session.
        if not sid:
            session = await self.store.create_ui_auth_session(
                clientdict, uri, method, description
            )

        else:
            try:
                session = await self.store.get_ui_auth_session(sid)
            except StoreError:
                raise SynapseError(400, "Unknown session ID: %s" % (sid,))

            if not clientdict:
                # 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 homeserver.
                # Revisit: Assuming the REST APIs do sensible validation, the data
                # isn't arbitrary.
                clientdict = session.clientdict

            # Ensure that the queried operation does not vary between stages of
            # the UI authentication session. This is done by generating a stable
            # comparator based on the URI, method, and body (minus the auth dict)
            # and storing it during the initial query. Subsequent queries ensure
            # that this comparator has not changed.
            comparator = (uri, method, clientdict)
            if (session.uri, session.method, session.clientdict) != comparator:
                raise SynapseError(
                    403,
                    "Requested operation has changed during the UI authentication session.",
                )

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

        # check auth type currently being presented
        errordict = {}  # type: Dict[str, Any]
        if "type" in authdict:
            login_type = authdict["type"]  # type: str
            try:
                result = await self._check_auth_dict(authdict, clientip)
                if result:
                    await self.store.mark_ui_auth_stage_complete(
                        session.session_id, login_type, result
                    )
            except LoginError as 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

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

        creds = await self.store.get_completed_ui_auth_stages(session.session_id)
        for f in flows:
            if len(set(f) - set(creds)) == 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,
                    list(clientdict),
                )

                return creds, clientdict, session.session_id

        ret = self._auth_dict_for_flows(flows, session.session_id)
        ret["completed"] = list(creds)
        ret.update(errordict)
        raise InteractiveAuthIncompleteError(ret)

    async def add_oob_auth(
        self, stagetype: str, authdict: Dict[str, Any], clientip: str
    ) -> bool:
        """
        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)

        result = await self.checkers[stagetype].check_auth(authdict, clientip)
        if result:
            await self.store.mark_ui_auth_stage_complete(
                authdict["session"], stagetype, result
            )
            return True
        return False

    def get_session_id(self, clientdict: Dict[str, Any]) -> Optional[str]:
        """
        Gets the session ID for a client given the client dictionary

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

        Returns:
            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

    async def set_session_data(self, session_id: str, key: str, value: Any) -> None:
        """
        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: The ID of this session as returned from check_auth
            key: The key to store the data under
            value: The data to store
        """
        try:
            await self.store.set_ui_auth_session_data(session_id, key, value)
        except StoreError:
            raise SynapseError(400, "Unknown session ID: %s" % (session_id,))

    async def get_session_data(
        self, session_id: str, key: str, default: Optional[Any] = None
    ) -> Any:
        """
        Retrieve data stored with set_session_data

        Args:
            session_id: The ID of this session as returned from check_auth
            key: The key to store the data under
            default: Value to return if the key has not been set
        """
        try:
            return await self.store.get_ui_auth_session_data(session_id, key, default)
        except StoreError:
            raise SynapseError(400, "Unknown session ID: %s" % (session_id,))

    async def _expire_old_sessions(self):
        """
        Invalidate any user interactive authentication sessions that have expired.
        """
        now = self._clock.time_msec()
        expiration_time = now - self.SESSION_EXPIRE_MS
        await self.store.delete_old_ui_auth_sessions(expiration_time)

    async def _check_auth_dict(
        self, authdict: Dict[str, Any], clientip: str
    ) -> Union[Dict[str, Any], str]:
        """Attempt to validate the auth dict provided by a client

        Args:
            authdict: auth dict provided by the client
            clientip: IP address of the client

        Returns:
            Result of the stage verification.

        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.
        """
        login_type = authdict["type"]
        checker = self.checkers.get(login_type)
        if checker is not None:
            res = await checker.check_auth(authdict, clientip=clientip)
            return res

        # build a v1-login-style dict out of the authdict and fall back to the
        # v1 code
        user_id = authdict.get("user")

        if user_id is None:
            raise SynapseError(400, "", Codes.MISSING_PARAM)

        (canonical_id, callback) = await self.validate_login(user_id, authdict)
        return canonical_id

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

    def _get_params_terms(self) -> dict:
        return {
            "policies": {
                "privacy_policy": {
                    "version": self.hs.config.user_consent_version,
                    "en": {
                        "name": self.hs.config.user_consent_policy_name,
                        "url": "%s_matrix/consent?v=%s"
                        % (
                            self.hs.config.public_baseurl,
                            self.hs.config.user_consent_version,
                        ),
                    },
                }
            }
        }

    def _auth_dict_for_flows(
        self, flows: List[List[str]], session_id: str,
    ) -> Dict[str, Any]:
        public_flows = []
        for f in flows:
            public_flows.append(f)

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

        params = {}  # type: Dict[str, Any]

        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,
        }

    async def get_access_token_for_user_id(
        self, user_id: str, device_id: Optional[str], valid_until_ms: Optional[int]
    ):
        """
        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: canonical User ID
            device_id: 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)
            valid_until_ms: when the token is valid until. None for
                no expiry.
        Returns:
              The access token for the user's session.
        Raises:
            StoreError if there was a problem storing the token.
        """
        fmt_expiry = ""
        if valid_until_ms is not None:
            fmt_expiry = time.strftime(
                " until %Y-%m-%d %H:%M:%S", time.localtime(valid_until_ms / 1000.0)
            )
        logger.info("Logging in user %s on device %s%s", user_id, device_id, fmt_expiry)

        await self.auth.check_auth_blocking(user_id)

        access_token = self.macaroon_gen.generate_access_token(user_id)
        await self.store.add_access_token_to_user(
            user_id, access_token, device_id, valid_until_ms
        )

        # 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:
                await self.store.get_device(user_id, device_id)
            except StoreError:
                await self.store.delete_access_token(access_token)
                raise StoreError(400, "Login raced against device deletion")

        return access_token

    async def check_user_exists(self, user_id: str) -> Optional[str]:
        """
        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:
            user_id: complete @user:id

        Returns:
            The canonical_user_id, or None if zero or multiple matches
        """
        res = await self._find_user_id_and_pwd_hash(user_id)
        if res is not None:
            return res[0]
        return None

    async def _find_user_id_and_pwd_hash(
        self, user_id: str
    ) -> Optional[Tuple[str, str]]:
        """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:
            A 2-tuple of `(canonical_user_id, password_hash)` or `None`
            if there is not exactly one match
        """
        user_infos = await self.store.get_users_by_id_case_insensitive(user_id)

        result = None
        if not user_infos:
            logger.warning("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.warning(
                "Attempted to login as %s but it matches more than one user "
                "inexactly: %r",
                user_id,
                user_infos.keys(),
            )
        return result

    def get_supported_login_types(self) -> Iterable[str]:
        """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:
            login types
        """
        return self._supported_login_types

    async def validate_login(
        self, username: str, login_submission: Dict[str, Any]
    ) -> Tuple[str, Optional[Callable[[Dict[str, str]], None]]]:
        """Authenticates the user for the /login API

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

        Args:
            username: username supplied by the user
            login_submission: the whole of the login submission
                (including 'type' and other relevant fields)
        Returns:
            A tuple of the 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 = await provider.check_password(qualified_user_id, password)
                if is_valid:
                    return 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 = await provider.check_auth(username, login_type, login_dict)
            if result:
                if isinstance(result, str):
                    result = (result, None)
                return result

        if login_type == LoginType.PASSWORD and self.hs.config.password_localdb_enabled:
            known_login_type = True

            canonical_user_id = await self._check_local_password(
                qualified_user_id, password  # type: ignore
            )

            if canonical_user_id:
                return canonical_user_id, None

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

        # 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)

    async def check_password_provider_3pid(
        self, medium: str, address: str, password: str
    ) -> Tuple[Optional[str], Optional[Callable[[Dict[str, str]], None]]]:
        """Check if a password provider is able to validate a thirdparty login

        Args:
            medium: The medium of the 3pid (ex. email).
            address: The address of the 3pid (ex. jdoe@example.com).
            password: The password of the user.

        Returns:
            A tuple of `(user_id, callback)`. If authentication is successful,
            `user_id`is the authenticated, canonical user ID. `callback` is
            then either a function to be later run after the server has
            completed login/registration, or `None`. If authentication was
            unsuccessful, `user_id` and `callback` are both `None`.
        """
        for provider in self.password_providers:
            if hasattr(provider, "check_3pid_auth"):
                # This function is able to return a deferred that either
                # resolves None, meaning authentication failure, or upon
                # success, to a str (which is the user_id) or a tuple of
                # (user_id, callback_func), where callback_func should be run
                # after we've finished everything else
                result = await provider.check_3pid_auth(medium, address, password)
                if result:
                    # Check if the return value is a str or a tuple
                    if isinstance(result, str):
                        # If it's a str, set callback function to None
                        result = (result, None)
                    return result

        return None, None

    async def _check_local_password(self, user_id: str, password: str) -> Optional[str]:
        """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: complete @user:id
            password: the provided password
        Returns:
            The canonical_user_id, or None if unknown user/bad password
        """
        lookupres = await self._find_user_id_and_pwd_hash(user_id)
        if not lookupres:
            return None
        (user_id, password_hash) = lookupres

        # If the password hash is None, the account has likely been deactivated
        if not password_hash:
            deactivated = await self.store.get_user_deactivated_status(user_id)
            if deactivated:
                raise UserDeactivatedError("This account has been deactivated")

        result = await self.validate_hash(password, password_hash)
        if not result:
            logger.warning("Failed password login for user %s", user_id)
            return None
        return user_id

    async def validate_short_term_login_token_and_get_user_id(self, login_token: str):
        auth_api = self.hs.get_auth()
        user_id = None
        try:
            macaroon = pymacaroons.Macaroon.deserialize(login_token)
            user_id = auth_api.get_user_id_from_macaroon(macaroon)
            auth_api.validate_macaroon(macaroon, "login", user_id)
        except Exception:
            raise AuthError(403, "Invalid token", errcode=Codes.FORBIDDEN)

        await self.auth.check_auth_blocking(user_id)
        return user_id

    async def delete_access_token(self, access_token: str):
        """Invalidate a single access token

        Args:
            access_token: access token to be deleted

        """
        user_info = await self.auth.get_user_by_access_token(access_token)
        await 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"):
                await 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:
            await self.hs.get_pusherpool().remove_pushers_by_access_token(
                str(user_info["user"]), (user_info["token_id"],)
            )

    async def delete_access_tokens_for_user(
        self,
        user_id: str,
        except_token_id: Optional[str] = None,
        device_id: Optional[str] = None,
    ):
        """Invalidate access tokens belonging to a user

        Args:
            user_id:  ID of user the tokens belong to
            except_token_id: access_token ID which should *not* be deleted
            device_id:  ID of device the tokens are associated with.
                If None, tokens associated with any device (or no device) will
                be deleted
        """
        tokens_and_devices = await 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:
                    await provider.on_logged_out(
                        user_id=user_id, device_id=device_id, access_token=token
                    )

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

    async def add_threepid(
        self, user_id: str, medium: str, address: str, validated_at: int
    ):
        # check if medium has a valid value
        if medium not in ["email", "msisdn"]:
            raise SynapseError(
                code=400,
                msg=("'%s' is not a valid value for 'medium'" % (medium,)),
                errcode=Codes.INVALID_PARAM,
            )

        # 'Canonicalise' email addresses down to lower case.
        # We've now moving towards the homeserver 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()

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

    async def delete_threepid(
        self, user_id: str, medium: str, address: str, id_server: Optional[str] = None
    ) -> bool:
        """Attempts to unbind the 3pid on the identity servers and deletes it
        from the local database.

        Args:
            user_id: ID of user to remove the 3pid from.
            medium: The medium of the 3pid being removed: "email" or "msisdn".
            address: The 3pid address to remove.
            id_server: Use the given identity server when unbinding
                any threepids. If None then will attempt to unbind using the
                identity server specified when binding (if known).

        Returns:
            Returns True if successfully unbound the 3pid on
            the identity server, False if identity server doesn't support the
            unbind API.
        """

        # 'Canonicalise' email addresses as per above
        if medium == "email":
            address = address.lower()

        identity_handler = self.hs.get_handlers().identity_handler
        result = await identity_handler.try_unbind_threepid(
            user_id, {"medium": medium, "address": address, "id_server": id_server}
        )

        await self.store.user_delete_threepid(user_id, medium, address)
        return result

    async def hash(self, password: str) -> str:
        """Computes a secure hash of password.

        Args:
            password: Password to hash.

        Returns:
            Hashed password.
        """

        def _do_hash():
            # Normalise the Unicode in the password
            pw = unicodedata.normalize("NFKC", password)

            return bcrypt.hashpw(
                pw.encode("utf8") + self.hs.config.password_pepper.encode("utf8"),
                bcrypt.gensalt(self.bcrypt_rounds),
            ).decode("ascii")

        return await defer_to_thread(self.hs.get_reactor(), _do_hash)

    async def validate_hash(
        self, password: str, stored_hash: Union[bytes, str]
    ) -> bool:
        """Validates that self.hash(password) == stored_hash.

        Args:
            password: Password to hash.
            stored_hash: Expected hash value.

        Returns:
            Whether self.hash(password) == stored_hash.
        """

        def _do_validate_hash():
            # Normalise the Unicode in the password
            pw = unicodedata.normalize("NFKC", password)

            return bcrypt.checkpw(
                pw.encode("utf8") + self.hs.config.password_pepper.encode("utf8"),
                stored_hash,
            )

        if stored_hash:
            if not isinstance(stored_hash, bytes):
                stored_hash = stored_hash.encode("ascii")

            return await defer_to_thread(self.hs.get_reactor(), _do_validate_hash)
        else:
            return False

    async def start_sso_ui_auth(self, redirect_url: str, session_id: str) -> str:
        """
        Get the HTML for the SSO redirect confirmation page.

        Args:
            redirect_url: The URL to redirect to the SSO provider.
            session_id: The user interactive authentication session ID.

        Returns:
            The HTML to render.
        """
        try:
            session = await self.store.get_ui_auth_session(session_id)
        except StoreError:
            raise SynapseError(400, "Unknown session ID: %s" % (session_id,))
        return self._sso_auth_confirm_template.render(
            description=session.description, redirect_url=redirect_url,
        )

    async def complete_sso_ui_auth(
        self, registered_user_id: str, session_id: str, request: SynapseRequest,
    ):
        """Having figured out a mxid for this user, complete the HTTP request

        Args:
            registered_user_id: The registered user ID to complete SSO login for.
            request: The request to complete.
            client_redirect_url: The URL to which to redirect the user at the end of the
                process.
        """
        # Mark the stage of the authentication as successful.
        # Save the user who authenticated with SSO, this will be used to ensure
        # that the account be modified is also the person who logged in.
        await self.store.mark_ui_auth_stage_complete(
            session_id, LoginType.SSO, registered_user_id
        )

        # Render the HTML and return.
        html_bytes = self._sso_auth_success_template.encode("utf-8")
        request.setResponseCode(200)
        request.setHeader(b"Content-Type", b"text/html; charset=utf-8")
        request.setHeader(b"Content-Length", b"%d" % (len(html_bytes),))

        request.write(html_bytes)
        finish_request(request)

    async def complete_sso_login(
        self,
        registered_user_id: str,
        request: SynapseRequest,
        client_redirect_url: str,
    ):
        """Having figured out a mxid for this user, complete the HTTP request

        Args:
            registered_user_id: The registered user ID to complete SSO login for.
            request: The request to complete.
            client_redirect_url: The URL to which to redirect the user at the end of the
                process.
        """
        # If the account has been deactivated, do not proceed with the login
        # flow.
        deactivated = await self.store.get_user_deactivated_status(registered_user_id)
        if deactivated:
            html_bytes = self._sso_account_deactivated_template.encode("utf-8")

            request.setResponseCode(403)
            request.setHeader(b"Content-Type", b"text/html; charset=utf-8")
            request.setHeader(b"Content-Length", b"%d" % (len(html_bytes),))
            request.write(html_bytes)
            finish_request(request)
            return

        self._complete_sso_login(registered_user_id, request, client_redirect_url)

    def _complete_sso_login(
        self,
        registered_user_id: str,
        request: SynapseRequest,
        client_redirect_url: str,
    ):
        """
        The synchronous portion of complete_sso_login.

        This exists purely for backwards compatibility of synapse.module_api.ModuleApi.
        """
        # Create a login token
        login_token = self.macaroon_gen.generate_short_term_login_token(
            registered_user_id
        )

        # Append the login token to the original redirect URL (i.e. with its query
        # parameters kept intact) to build the URL to which the template needs to
        # redirect the users once they have clicked on the confirmation link.
        redirect_url = self.add_query_param_to_url(
            client_redirect_url, "loginToken", login_token
        )

        # if the client is whitelisted, we can redirect straight to it
        if client_redirect_url.startswith(self._whitelisted_sso_clients):
            request.redirect(redirect_url)
            finish_request(request)
            return

        # Otherwise, serve the redirect confirmation page.

        # Remove the query parameters from the redirect URL to get a shorter version of
        # it. This is only to display a human-readable URL in the template, but not the
        # URL we redirect users to.
        redirect_url_no_params = client_redirect_url.split("?")[0]

        html_bytes = self._sso_redirect_confirm_template.render(
            display_url=redirect_url_no_params,
            redirect_url=redirect_url,
            server_name=self._server_name,
        ).encode("utf-8")

        request.setResponseCode(200)
        request.setHeader(b"Content-Type", b"text/html; charset=utf-8")
        request.setHeader(b"Content-Length", b"%d" % (len(html_bytes),))
        request.write(html_bytes)
        finish_request(request)

    @staticmethod
    def add_query_param_to_url(url: str, param_name: str, param: Any):
        url_parts = list(urllib.parse.urlparse(url))
        query = dict(urllib.parse.parse_qsl(url_parts[4]))
        query.update({param_name: param})
        url_parts[4] = urllib.parse.urlencode(query)
        return urllib.parse.urlunparse(url_parts)


@attr.s
class MacaroonGenerator(object):

    hs = attr.ib()

    def generate_access_token(
        self, user_id: str, extra_caveats: Optional[List[str]] = None
    ) -> str:
        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: str, duration_in_ms: int = (2 * 60 * 1000)
    ) -> str:
        macaroon = self._generate_base_macaroon(user_id)
        macaroon.add_first_party_caveat("type = login")
        now = self.hs.get_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: str) -> str:
        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: str) -> pymacaroons.Macaroon:
        macaroon = pymacaroons.Macaroon(
            location=self.hs.config.server_name,
            identifier="key",
            key=self.hs.config.macaroon_secret_key,
        )
        macaroon.add_first_party_caveat("gen = 1")
        macaroon.add_first_party_caveat("user_id = %s" % (user_id,))
        return macaroon