# -*- 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.

from twisted.internet import defer

from ._base import BaseHandler
from synapse.api.constants import LoginType
from synapse.types import UserID
from synapse.api.errors import AuthError, LoginError, Codes, StoreError, SynapseError
from synapse.util.async import run_on_reactor
from synapse.config.ldap import LDAPMode

from twisted.web.client import PartialDownloadError

import logging
import bcrypt
import pymacaroons
import simplejson

try:
    import ldap3
except ImportError:
    ldap3 = None
    pass

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.DUMMY: self._check_dummy_auth,
        }
        self.bcrypt_rounds = hs.config.bcrypt_rounds
        self.sessions = {}

        self.ldap_enabled = hs.config.ldap_enabled
        if self.ldap_enabled:
            if not ldap3:
                raise RuntimeError(
                    'Missing ldap3 library. This is required for LDAP Authentication.'
                )
            self.ldap_mode = hs.config.ldap_mode
            self.ldap_uri = hs.config.ldap_uri
            self.ldap_start_tls = hs.config.ldap_start_tls
            self.ldap_base = hs.config.ldap_base
            self.ldap_attributes = hs.config.ldap_attributes
            if self.ldap_mode == LDAPMode.SEARCH:
                self.ldap_bind_dn = hs.config.ldap_bind_dn
                self.ldap_bind_password = hs.config.ldap_bind_password
                self.ldap_filter = hs.config.ldap_filter

        self.hs = hs  # FIXME better possibility to access registrationHandler later?
        self.device_handler = hs.get_device_handler()

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

        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:
            A tuple of (authed, dict, dict, session_id) where authed is true if
            the client has successfully completed an auth flow. If it is true
            the first dict contains the authenticated credentials of each stage.

            If authed is false, the first dictionary is the server response to
            the login request and should be passed back to the client.

            In either case, the second dict 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 the call to check_auth
        """

        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:
            defer.returnValue(
                (
                    False, self._auth_dict_for_flows(flows, session),
                    clientdict, session['id']
                )
            )

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

        # check auth type currently being presented
        errordict = {}
        if 'type' in authdict:
            if authdict['type'] not in self.checkers:
                raise LoginError(400, "", Codes.UNRECOGNIZED)
            try:
                result = yield self.checkers[authdict['type']](authdict, clientip)
                if result:
                    creds[authdict['type']] = result
                    self._save_session(session)
            except LoginError, 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:
                logger.info("Auth completed with creds: %r", creds)
                defer.returnValue((True, creds, clientdict, session['id']))

        ret = self._auth_dict_for_flows(flows, session)
        ret['completed'] = creds.keys()
        ret.update(errordict)
        defer.returnValue((False, ret, clientdict, session['id']))

    @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)

    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"]
        if not user_id.startswith('@'):
            user_id = UserID.create(user_id, self.hs.hostname).to_string()

        return self._check_password(user_id, password)

    @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)

    @defer.inlineCallbacks
    def _check_email_identity(self, 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)

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

        defer.returnValue(threepid)

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

    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]

    def validate_password_login(self, user_id, password):
        """
        Authenticates the user with their username and password.

        Used only by the v1 login API.

        Args:
            user_id (str): complete @user:id
            password (str): Password
        Returns:
            defer.Deferred: (str) canonical user id
        Raises:
            StoreError if there was a problem accessing the database
            LoginError if there was an authentication problem.
        """
        return self._check_password(user_id, password)

    @defer.inlineCallbacks
    def get_login_tuple_for_user_id(self, user_id, device_id=None,
                                    initial_display_name=None):
        """
        Gets login tuple for the user with the given user ID.

        Creates a new access/refresh token for the user.

        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)
            initial_display_name (str): display name to associate with the
               device if it needs re-registering
        Returns:
            A tuple of:
              The access token for the user's session.
              The refresh token for the user's session.
        Raises:
            StoreError if there was a problem storing the token.
            LoginError if there was an authentication problem.
        """
        logger.info("Logging in user %s on device %s", user_id, device_id)
        access_token = yield self.issue_access_token(user_id, device_id)
        refresh_token = yield self.issue_refresh_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:
            yield self.device_handler.check_device_registered(
                user_id, device_id, initial_display_name
            )

        defer.returnValue((access_token, refresh_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)

    @defer.inlineCallbacks
    def _check_password(self, user_id, password):
        """Authenticate a user against the LDAP and local databases.

        user_id is checked case insensitively against the local database, but
        will throw if there are multiple inexact matches.

        Args:
            user_id (str): complete @user:id
        Returns:
            (str) the canonical_user_id
        Raises:
            LoginError if login fails
        """
        valid_ldap = yield self._check_ldap_password(user_id, password)
        if valid_ldap:
            defer.returnValue(user_id)

        canonical_user_id = yield self._check_local_password(user_id, password)

        if canonical_user_id:
            defer.returnValue(canonical_user_id)

        # 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 _check_ldap_password(self, user_id, password):
        """ Attempt to authenticate a user against an LDAP Server
            and register an account if none exists.

            Returns:
                True if authentication against LDAP was successful
        """

        if not ldap3 or not self.ldap_enabled:
            defer.returnValue(False)

        if self.ldap_mode not in LDAPMode.LIST:
            raise RuntimeError(
                'Invalid ldap mode specified: {mode}'.format(
                    mode=self.ldap_mode
                )
            )

        try:
            server = ldap3.Server(self.ldap_uri)
            logger.debug(
                "Attempting ldap connection with %s",
                self.ldap_uri
            )

            localpart = UserID.from_string(user_id).localpart
            if self.ldap_mode == LDAPMode.SIMPLE:
                # bind with the the local users ldap credentials
                bind_dn = "{prop}={value},{base}".format(
                    prop=self.ldap_attributes['uid'],
                    value=localpart,
                    base=self.ldap_base
                )
                conn = ldap3.Connection(server, bind_dn, password)
                logger.debug(
                    "Established ldap connection in simple mode: %s",
                    conn
                )

                if self.ldap_start_tls:
                    conn.start_tls()
                    logger.debug(
                        "Upgraded ldap connection in simple mode through StartTLS: %s",
                        conn
                    )

                conn.bind()

            elif self.ldap_mode == LDAPMode.SEARCH:
                # connect with preconfigured credentials and search for local user
                conn = ldap3.Connection(
                    server,
                    self.ldap_bind_dn,
                    self.ldap_bind_password
                )
                logger.debug(
                    "Established ldap connection in search mode: %s",
                    conn
                )

                if self.ldap_start_tls:
                    conn.start_tls()
                    logger.debug(
                        "Upgraded ldap connection in search mode through StartTLS: %s",
                        conn
                    )

                conn.bind()

                # find matching dn
                query = "({prop}={value})".format(
                    prop=self.ldap_attributes['uid'],
                    value=localpart
                )
                if self.ldap_filter:
                    query = "(&{query}{filter})".format(
                        query=query,
                        filter=self.ldap_filter
                    )
                logger.debug("ldap search filter: %s", query)
                result = conn.search(self.ldap_base, query)

                if result and len(conn.response) == 1:
                    # found exactly one result
                    user_dn = conn.response[0]['dn']
                    logger.debug('ldap search found dn: %s', user_dn)

                    # unbind and reconnect, rebind with found dn
                    conn.unbind()
                    conn = ldap3.Connection(
                        server,
                        user_dn,
                        password,
                        auto_bind=True
                    )
                else:
                    # found 0 or > 1 results, abort!
                    logger.warn(
                        "ldap search returned unexpected (%d!=1) amount of results",
                        len(conn.response)
                    )
                    defer.returnValue(False)

            logger.info(
                "User authenticated against ldap server: %s",
                conn
            )

            # check for existing account, if none exists, create one
            if not (yield self.check_user_exists(user_id)):
                # query user metadata for account creation
                query = "({prop}={value})".format(
                    prop=self.ldap_attributes['uid'],
                    value=localpart
                )

                if self.ldap_mode == LDAPMode.SEARCH and self.ldap_filter:
                    query = "(&{filter}{user_filter})".format(
                        filter=query,
                        user_filter=self.ldap_filter
                    )
                logger.debug("ldap registration filter: %s", query)

                result = conn.search(
                    search_base=self.ldap_base,
                    search_filter=query,
                    attributes=[
                        self.ldap_attributes['name'],
                        self.ldap_attributes['mail']
                    ]
                )

                if len(conn.response) == 1:
                    attrs = conn.response[0]['attributes']
                    mail = attrs[self.ldap_attributes['mail']][0]
                    name = attrs[self.ldap_attributes['name']][0]

                    # create account
                    registration_handler = self.hs.get_handlers().registration_handler
                    user_id, access_token = (
                        yield registration_handler.register(localpart=localpart)
                    )

                    # TODO: bind email, set displayname with data from ldap directory

                    logger.info(
                        "ldap registration successful: %d: %s (%s, %)",
                        user_id,
                        localpart,
                        name,
                        mail
                    )
                else:
                    logger.warn(
                        "ldap registration failed: unexpected (%d!=1) amount of results",
                        len(conn.response)
                    )
                    defer.returnValue(False)

            defer.returnValue(True)
        except ldap3.core.exceptions.LDAPException as e:
            logger.warn("Error during ldap authentication: %s", e)
            defer.returnValue(False)

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

    @defer.inlineCallbacks
    def issue_refresh_token(self, user_id, device_id=None):
        refresh_token = self.generate_refresh_token(user_id)
        yield self.store.add_refresh_token_to_user(user_id, refresh_token,
                                                   device_id)
        defer.returnValue(refresh_token)

    def generate_access_token(self, user_id, extra_caveats=None,
                              duration_in_ms=(60 * 60 * 1000)):
        extra_caveats = extra_caveats or []
        macaroon = self._generate_base_macaroon(user_id)
        macaroon.add_first_party_caveat("type = access")
        now = self.hs.get_clock().time_msec()
        expiry = now + duration_in_ms
        macaroon.add_first_party_caveat("time < %d" % (expiry,))
        for caveat in extra_caveats:
            macaroon.add_first_party_caveat(caveat)
        return macaroon.serialize()

    def generate_refresh_token(self, user_id):
        m = self._generate_base_macaroon(user_id)
        m.add_first_party_caveat("type = refresh")
        # Important to add a nonce, because otherwise every refresh token for a
        # user will be the same.
        m.add_first_party_caveat("nonce = %s" % (
            stringutils.random_string_with_symbols(16),
        ))
        return m.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.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):
        macaroon = self._generate_base_macaroon(user_id)
        macaroon.add_first_party_caveat("type = delete_pusher")
        return macaroon.serialize()

    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)

    def _generate_base_macaroon(self, user_id):
        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

    @defer.inlineCallbacks
    def set_password(self, user_id, newpassword, requester=None):
        password_hash = self.hash(newpassword)

        except_access_token_id = requester.access_token_id if requester else None

        try:
            yield self.store.user_set_password_hash(user_id, password_hash)
        except StoreError as e:
            if e.code == 404:
                raise SynapseError(404, "Unknown user", Codes.NOT_FOUND)
            raise e
        yield self.store.user_delete_access_tokens(
            user_id, except_access_token_id
        )
        yield self.hs.get_pusherpool().remove_pushers_by_user(
            user_id, except_access_token_id
        )

    @defer.inlineCallbacks
    def add_threepid(self, user_id, medium, address, validated_at):
        yield self.store.user_add_threepid(
            user_id, medium, address, validated_at,
            self.hs.get_clock().time_msec()
        )

    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
        self._prune_sessions()

    def _prune_sessions(self):
        for sid, sess in self.sessions.items():
            last_used = 0
            if 'last_used' in sess:
                last_used = sess['last_used']
            now = self.hs.get_clock().time_msec()
            if last_used < now - AuthHandler.SESSION_EXPIRE_MS:
                del self.sessions[sid]

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

        Args:
            password (str): Password to hash.

        Returns:
            Hashed password (str).
        """
        return bcrypt.hashpw(password + 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 + self.hs.config.password_pepper,
                                 stored_hash.encode('utf-8')) == stored_hash
        else:
            return False