#
# This file is licensed under the Affero General Public License (AGPL) version 3.
#
# Copyright 2017 Vector Creations Ltd
# Copyright 2015 - 2016 OpenMarket Ltd
# Copyright (C) 2023 New Vector, Ltd
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License as
# published by the Free Software Foundation, either version 3 of the
# License, or (at your option) any later version.
#
# See the GNU Affero General Public License for more details:
# <https://www.gnu.org/licenses/agpl-3.0.html>.
#
# Originally licensed under the Apache License, Version 2.0:
# <http://www.apache.org/licenses/LICENSE-2.0>.
#
# [This file includes modifications made by New Vector Limited]
#
#
import logging
import random
from typing import TYPE_CHECKING

from twisted.web.server import Request

import synapse
import synapse.api.auth
import synapse.types
from synapse.api.constants import (
    APP_SERVICE_REGISTRATION_TYPE,
    ApprovalNoticeMedium,
    LoginType,
)
from synapse.api.errors import (
    Codes,
    InteractiveAuthIncompleteError,
    NotApprovedError,
    SynapseError,
    ThreepidValidationError,
    UnrecognizedRequestError,
)
from synapse.api.ratelimiting import Ratelimiter
from synapse.config import ConfigError
from synapse.config.homeserver import HomeServerConfig
from synapse.config.ratelimiting import FederationRatelimitSettings
from synapse.config.server import is_threepid_reserved
from synapse.handlers.auth import AuthHandler
from synapse.handlers.ui_auth import UIAuthSessionDataConstants
from synapse.http.server import HttpServer, finish_request, respond_with_html
from synapse.http.servlet import (
    RestServlet,
    assert_params_in_dict,
    parse_json_object_from_request,
    parse_string,
)
from synapse.http.site import SynapseRequest
from synapse.metrics import SERVER_NAME_LABEL, threepid_send_requests
from synapse.push.mailer import Mailer
from synapse.types import JsonDict
from synapse.util.duration import Duration
from synapse.util.msisdn import phone_number_to_msisdn
from synapse.util.ratelimitutils import FederationRateLimiter
from synapse.util.stringutils import assert_valid_client_secret, random_string
from synapse.util.threepids import (
    canonicalise_email,
    check_3pid_allowed,
    validate_email,
)

from ._base import client_patterns, interactive_auth_handler

if TYPE_CHECKING:
    from synapse.server import HomeServer

logger = logging.getLogger(__name__)


class EmailRegisterRequestTokenRestServlet(RestServlet):
    PATTERNS = client_patterns("/register/email/requestToken$")

    def __init__(self, hs: "HomeServer"):
        super().__init__()
        self.hs = hs
        self.server_name = hs.hostname
        self.identity_handler = hs.get_identity_handler()
        self.config = hs.config
        self._registration_enabled = hs.config.registration.enable_registration

        if self.hs.config.email.can_verify_email:
            self.registration_mailer = Mailer(
                hs=self.hs,
                app_name=self.config.email.email_app_name,
                template_html=self.config.email.email_registration_template_html,
                template_text=self.config.email.email_registration_template_text,
            )
            self.already_in_use_mailer = Mailer(
                hs=self.hs,
                app_name=self.config.email.email_app_name,
                template_html=self.config.email.email_already_in_use_template_html,
                template_text=self.config.email.email_already_in_use_template_text,
            )

    async def on_POST(self, request: SynapseRequest) -> tuple[int, JsonDict]:
        if not self.hs.config.email.can_verify_email:
            logger.warning(
                "Email registration has been disabled due to lack of email config"
            )
            raise SynapseError(
                400, "Email-based registration has been disabled on this server"
            )

        if not self._registration_enabled:
            raise SynapseError(
                403,
                "Registration is disabled on this homeserver",
                Codes.FORBIDDEN,
            )

        body = parse_json_object_from_request(request)

        assert_params_in_dict(body, ["client_secret", "email", "send_attempt"])

        # Extract params from body
        client_secret = body["client_secret"]
        assert_valid_client_secret(client_secret)

        # For emails, canonicalise the address.
        # We store all email addresses canonicalised in the DB.
        # (See on_POST in EmailThreepidRequestTokenRestServlet
        # in synapse/rest/client/account.py)
        try:
            email = validate_email(body["email"])
        except ValueError as e:
            raise SynapseError(400, str(e))
        send_attempt = body["send_attempt"]
        next_link = body.get("next_link")  # Optional param

        if not await check_3pid_allowed(self.hs, "email", email, registration=True):
            raise SynapseError(
                403,
                "Your email domain is not authorized to register on this server",
                Codes.THREEPID_DENIED,
            )

        await self.identity_handler.ratelimit_request_token_requests(
            request, "email", email
        )

        existing_user_id = await self.hs.get_datastores().main.get_user_id_by_threepid(
            "email", email
        )

        if existing_user_id is not None:
            if self.hs.config.server.request_token_inhibit_3pid_errors:
                # Make the client think the operation succeeded. See the rationale in the
                # comments for request_token_inhibit_3pid_errors.
                # Still send an email to warn the user that an account already exists.
                # Also wait for some random amount of time between 100ms and 1s to make it
                # look like we did something.
                await self.already_in_use_mailer.send_already_in_use_mail(email)
                await self.hs.get_clock().sleep(
                    Duration(milliseconds=random.randint(100, 1000))
                )
                return 200, {"sid": random_string(16)}

            raise SynapseError(400, "Email is already in use", Codes.THREEPID_IN_USE)

        # Send registration emails from Synapse
        sid = await self.identity_handler.send_threepid_validation(
            email,
            client_secret,
            send_attempt,
            self.registration_mailer.send_registration_mail,
            next_link,
        )

        threepid_send_requests.labels(
            type="email",
            reason="register",
            **{SERVER_NAME_LABEL: self.server_name},
        ).observe(send_attempt)

        # Wrap the session id in a JSON object
        return 200, {"sid": sid}


class MsisdnRegisterRequestTokenRestServlet(RestServlet):
    PATTERNS = client_patterns("/register/msisdn/requestToken$")

    def __init__(self, hs: "HomeServer"):
        super().__init__()
        self.hs = hs
        self.server_name = hs.hostname
        self.identity_handler = hs.get_identity_handler()

    async def on_POST(self, request: SynapseRequest) -> tuple[int, JsonDict]:
        body = parse_json_object_from_request(request)

        assert_params_in_dict(
            body, ["client_secret", "country", "phone_number", "send_attempt"]
        )
        client_secret = body["client_secret"]
        assert_valid_client_secret(client_secret)
        country = body["country"]
        phone_number = body["phone_number"]
        send_attempt = body["send_attempt"]
        next_link = body.get("next_link")  # Optional param

        msisdn = phone_number_to_msisdn(country, phone_number)

        if not await check_3pid_allowed(self.hs, "msisdn", msisdn, registration=True):
            raise SynapseError(
                403,
                "Phone numbers are not authorized to register on this server",
                Codes.THREEPID_DENIED,
            )

        await self.identity_handler.ratelimit_request_token_requests(
            request, "msisdn", msisdn
        )

        existing_user_id = await self.hs.get_datastores().main.get_user_id_by_threepid(
            "msisdn", msisdn
        )

        if existing_user_id is not None:
            if self.hs.config.server.request_token_inhibit_3pid_errors:
                # Make the client think the operation succeeded. See the rationale in the
                # comments for request_token_inhibit_3pid_errors.
                # Also wait for some random amount of time between 100ms and 1s to make it
                # look like we did something.
                await self.hs.get_clock().sleep(
                    Duration(milliseconds=random.randint(100, 1000))
                )
                return 200, {"sid": random_string(16)}

            raise SynapseError(
                400, "Phone number is already in use", Codes.THREEPID_IN_USE
            )

        if not self.hs.config.registration.account_threepid_delegate_msisdn:
            logger.warning(
                "No upstream msisdn account_threepid_delegate configured on the server to "
                "handle this request"
            )
            raise SynapseError(
                400, "Registration by phone number is not supported on this homeserver"
            )

        ret = await self.identity_handler.requestMsisdnToken(
            self.hs.config.registration.account_threepid_delegate_msisdn,
            country,
            phone_number,
            client_secret,
            send_attempt,
            next_link,
        )

        threepid_send_requests.labels(
            type="msisdn",
            reason="register",
            **{SERVER_NAME_LABEL: self.server_name},
        ).observe(send_attempt)

        return 200, ret


class RegistrationSubmitTokenServlet(RestServlet):
    """Handles registration 3PID validation token submission"""

    PATTERNS = client_patterns(
        "/registration/(?P<medium>[^/]*)/submit_token$", releases=(), unstable=True
    )

    def __init__(self, hs: "HomeServer"):
        super().__init__()
        self.hs = hs
        self.auth = hs.get_auth()
        self.config = hs.config
        self.clock = hs.get_clock()
        self.store = hs.get_datastores().main

        if self.config.email.can_verify_email:
            self._failure_email_template = (
                self.config.email.email_registration_template_failure_html
            )

    async def on_GET(self, request: Request, medium: str) -> None:
        if medium != "email":
            raise SynapseError(
                400, "This medium is currently not supported for registration"
            )
        if not self.config.email.can_verify_email:
            logger.warning(
                "User registration via email has been disabled due to lack of email config"
            )
            raise SynapseError(
                400, "Email-based registration is disabled on this server"
            )

        sid = parse_string(request, "sid", required=True)
        client_secret = parse_string(request, "client_secret", required=True)
        assert_valid_client_secret(client_secret)
        token = parse_string(request, "token", required=True)

        # Attempt to validate a 3PID session
        try:
            # Mark the session as valid
            next_link = await self.store.validate_threepid_session(
                sid, client_secret, token, self.clock.time_msec()
            )

            # Perform a 302 redirect if next_link is set
            if next_link:
                if next_link.startswith("file:///"):
                    logger.warning(
                        "Not redirecting to next_link as it is a local file: address"
                    )
                else:
                    request.setResponseCode(302)
                    request.setHeader("Location", next_link)
                    finish_request(request)
                    return None

            # Otherwise show the success template
            html = self.config.email.email_registration_template_success_html_content
            status_code = 200
        except ThreepidValidationError as e:
            status_code = e.code

            # Show a failure page with a reason
            template_vars = {"failure_reason": e.msg}
            html = self._failure_email_template.render(**template_vars)

        respond_with_html(request, status_code, html)


class UsernameAvailabilityRestServlet(RestServlet):
    PATTERNS = client_patterns("/register/available")

    def __init__(self, hs: "HomeServer"):
        super().__init__()
        self.hs = hs
        self.server_name = hs.hostname
        self.registration_handler = hs.get_registration_handler()
        self.ratelimiter = FederationRateLimiter(
            our_server_name=self.server_name,
            clock=hs.get_clock(),
            config=FederationRatelimitSettings(
                # Time window of 2s
                window_size=2000,
                # Artificially delay requests if rate > sleep_limit/window_size
                sleep_limit=1,
                # Amount of artificial delay to apply
                sleep_delay=1000,
                # Error with 429 if more than reject_limit requests are queued
                reject_limit=1,
                # Allow 1 request at a time
                concurrent=1,
            ),
        )

        self.inhibit_user_in_use_error = (
            hs.config.registration.inhibit_user_in_use_error
        )

    async def on_GET(self, request: Request) -> tuple[int, JsonDict]:
        if not self.hs.config.registration.enable_registration:
            raise SynapseError(
                403, "Registration has been disabled", errcode=Codes.FORBIDDEN
            )

        if self.inhibit_user_in_use_error:
            return 200, {"available": True}

        ip = request.getClientAddress().host
        with self.ratelimiter.ratelimit(ip) as wait_deferred:
            await wait_deferred

            username = parse_string(request, "username", required=True)

            await self.registration_handler.check_username(username)

            return 200, {"available": True}


class RegistrationTokenValidityRestServlet(RestServlet):
    """Check the validity of a registration token.

    Example:

        GET /_matrix/client/v1/register/m.login.registration_token/validity?token=abcd

        200 OK

        {
            "valid": true
        }
    """

    PATTERNS = client_patterns(
        f"/register/{LoginType.REGISTRATION_TOKEN}/validity",
        releases=("v1",),
    )
    CATEGORY = "Registration/login requests"

    def __init__(self, hs: "HomeServer"):
        super().__init__()
        self.hs = hs
        self.store = hs.get_datastores().main
        self.ratelimiter = Ratelimiter(
            store=self.store,
            clock=hs.get_clock(),
            cfg=hs.config.ratelimiting.rc_registration_token_validity,
        )

    async def on_GET(self, request: Request) -> tuple[int, JsonDict]:
        await self.ratelimiter.ratelimit(None, (request.getClientAddress().host,))

        if not self.hs.config.registration.enable_registration:
            raise SynapseError(
                403, "Registration has been disabled", errcode=Codes.FORBIDDEN
            )

        token = parse_string(request, "token", required=True)
        valid = await self.store.registration_token_is_valid(token)

        return 200, {"valid": valid}


class RegisterRestServlet(RestServlet):
    PATTERNS = client_patterns("/register$")
    CATEGORY = "Registration/login requests"

    def __init__(self, hs: "HomeServer"):
        super().__init__()

        self.hs = hs
        self.auth = hs.get_auth()
        self.store = hs.get_datastores().main
        self.auth_handler = hs.get_auth_handler()
        self.registration_handler = hs.get_registration_handler()
        self.identity_handler = hs.get_identity_handler()
        self.room_member_handler = hs.get_room_member_handler()
        self.macaroon_gen = hs.get_macaroon_generator()
        self.ratelimiter = hs.get_registration_ratelimiter()
        self.password_policy_handler = hs.get_password_policy_handler()
        self.clock = hs.get_clock()
        self.password_auth_provider = hs.get_password_auth_provider()
        self._registration_enabled = self.hs.config.registration.enable_registration
        self._refresh_tokens_enabled = (
            hs.config.registration.refreshable_access_token_lifetime is not None
        )
        self._inhibit_user_in_use_error = (
            hs.config.registration.inhibit_user_in_use_error
        )

        self._require_approval = (
            hs.config.experimental.msc3866.enabled
            and hs.config.experimental.msc3866.require_approval_for_new_accounts
        )

        self._registration_flows = _calculate_registration_flows(
            hs.config, self.auth_handler
        )

    @interactive_auth_handler
    async def on_POST(self, request: SynapseRequest) -> tuple[int, JsonDict]:
        body = parse_json_object_from_request(request)

        client_addr = request.getClientAddress().host

        await self.ratelimiter.ratelimit(None, client_addr, update=False)

        kind = parse_string(request, "kind", default="user")

        if kind == "guest":
            ret = await self._do_guest_registration(body, address=client_addr)
            return ret
        elif kind != "user":
            raise UnrecognizedRequestError(
                f"Do not understand membership kind: {kind}",
            )

        # Check if the clients wishes for this registration to issue a refresh
        # token.
        client_requested_refresh_tokens = body.get("refresh_token", False)
        if not isinstance(client_requested_refresh_tokens, bool):
            raise SynapseError(400, "`refresh_token` should be true or false.")

        should_issue_refresh_token = (
            self._refresh_tokens_enabled and client_requested_refresh_tokens
        )

        # Pull out the provided username and do basic sanity checks early since
        # the auth layer will store these in sessions.
        desired_username = None
        if "username" in body:
            desired_username = body["username"]
            if not isinstance(desired_username, str) or len(desired_username) > 512:
                raise SynapseError(400, "Invalid username")

        # fork off as soon as possible for ASes which have completely
        # different registration flows to normal users

        # == Application Service Registration ==
        if body.get("type") == APP_SERVICE_REGISTRATION_TYPE:
            if not self.auth.has_access_token(request):
                raise SynapseError(
                    400,
                    "Appservice token must be provided when using a type of m.login.application_service",
                )

            # XXX we should check that desired_username is valid. Currently
            # we give appservices carte blanche for any insanity in mxids,
            # because the IRC bridges rely on being able to register stupid
            # IDs.

            access_token = self.auth.get_access_token_from_request(request)

            # Desired username is either a string or None.
            if desired_username is None:
                raise SynapseError(400, "Desired Username is missing or not a string")

            result = await self._do_appservice_registration(
                desired_username,
                access_token,
                body,
                should_issue_refresh_token=should_issue_refresh_token,
            )

            return 200, result
        elif self.auth.has_access_token(request):
            raise SynapseError(
                400,
                "An access token should not be provided on requests to /register (except if type is m.login.application_service)",
            )

        # == Normal User Registration == (everyone else)
        if not self._registration_enabled:
            raise SynapseError(403, "Registration has been disabled", Codes.FORBIDDEN)

        # For regular registration, convert the provided username to lowercase
        # before attempting to register it. This should mean that people who try
        # to register with upper-case in their usernames don't get a nasty surprise.
        #
        # Note that we treat usernames case-insensitively in login, so they are
        # free to carry on imagining that their username is CrAzYh4cKeR if that
        # keeps them happy.
        if desired_username is not None:
            desired_username = desired_username.lower()

        # Check if this account is upgrading from a guest account.
        guest_access_token = body.get("guest_access_token", None)

        # Pull out the provided password and do basic sanity checks early.
        #
        # Note that we remove the password from the body since the auth layer
        # will store the body in the session and we don't want a plaintext
        # password store there.
        password = body.pop("password", None)
        if password is not None:
            if not isinstance(password, str) or len(password) > 512:
                raise SynapseError(400, "Invalid password")
            self.password_policy_handler.validate_password(password)

        if "initial_device_display_name" in body and password is None:
            # ignore 'initial_device_display_name' if sent without
            # a password to work around a client bug where it sent
            # the 'initial_device_display_name' param alone, wiping out
            # the original registration params
            logger.warning("Ignoring initial_device_display_name without password")
            del body["initial_device_display_name"]

        session_id = self.auth_handler.get_session_id(body)
        registered_user_id = None
        password_hash = None
        if session_id:
            # if we get a registered user id out of here, it means we previously
            # registered a user for this session, so we could just return the
            # user here. We carry on and go through the auth checks though,
            # for paranoia.
            registered_user_id = await self.auth_handler.get_session_data(
                session_id, UIAuthSessionDataConstants.REGISTERED_USER_ID, None
            )
            # Extract the previously-hashed password from the session.
            password_hash = await self.auth_handler.get_session_data(
                session_id, UIAuthSessionDataConstants.PASSWORD_HASH, None
            )

        # Ensure that the username is valid.
        if desired_username is not None:
            await self.registration_handler.check_username(
                desired_username,
                guest_access_token=guest_access_token,
                assigned_user_id=registered_user_id,
                inhibit_user_in_use_error=self._inhibit_user_in_use_error,
            )

        # Check if the user-interactive authentication flows are complete, if
        # not this will raise a user-interactive auth error.
        try:
            auth_result, params, session_id = await self.auth_handler.check_ui_auth(
                self._registration_flows,
                request,
                body,
                "register a new account",
            )
        except InteractiveAuthIncompleteError as e:
            # The user needs to provide more steps to complete auth.
            #
            # Hash the password and store it with the session since the client
            # is not required to provide the password again.
            #
            # If a password hash was previously stored we will not attempt to
            # re-hash and store it for efficiency. This assumes the password
            # does not change throughout the authentication flow, but this
            # should be fine since the data is meant to be consistent.
            if not password_hash and password:
                password_hash = await self.auth_handler.hash(password)
                await self.auth_handler.set_session_data(
                    e.session_id,
                    UIAuthSessionDataConstants.PASSWORD_HASH,
                    password_hash,
                )
            raise

        # Check that we're not trying to register a denied 3pid.
        #
        # the user-facing checks will probably already have happened in
        # /register/email/requestToken when we requested a 3pid, but that's not
        # guaranteed.
        if auth_result:
            for login_type in [LoginType.EMAIL_IDENTITY, LoginType.MSISDN]:
                if login_type in auth_result:
                    medium = auth_result[login_type]["medium"]
                    address = auth_result[login_type]["address"]

                    if not await check_3pid_allowed(
                        self.hs, medium, address, registration=True
                    ):
                        raise SynapseError(
                            403,
                            "Third party identifiers (email/phone numbers)"
                            + " are not authorized on this server",
                            Codes.THREEPID_DENIED,
                        )

        if registered_user_id is not None:
            logger.info(
                "Already registered user ID %r for this session", registered_user_id
            )
            # don't re-register the threepids
            registered = False
        else:
            # If we have a password in this request, prefer it. Otherwise, there
            # might be a password hash from an earlier request.
            if password:
                password_hash = await self.auth_handler.hash(password)
            if not password_hash:
                raise SynapseError(400, "Missing params: password", Codes.MISSING_PARAM)

            desired_username = await (
                self.password_auth_provider.get_username_for_registration(
                    auth_result,
                    params,
                )
            )

            if desired_username is None:
                desired_username = params.get("username", None)

            guest_access_token = params.get("guest_access_token", None)

            if desired_username is not None:
                desired_username = desired_username.lower()

            threepid = None
            if auth_result:
                threepid = auth_result.get(LoginType.EMAIL_IDENTITY)

                # Also check that we're not trying to register a 3pid that's already
                # been registered.
                #
                # This has probably happened in /register/email/requestToken as well,
                # but if a user hits this endpoint twice then clicks on each link from
                # the two activation emails, they would register the same 3pid twice.
                for login_type in [LoginType.EMAIL_IDENTITY, LoginType.MSISDN]:
                    if login_type in auth_result:
                        medium = auth_result[login_type]["medium"]
                        address = auth_result[login_type]["address"]
                        # For emails, canonicalise the address.
                        # We store all email addresses canonicalised in the DB.
                        # (See on_POST in EmailThreepidRequestTokenRestServlet
                        # in synapse/rest/client/account.py)
                        if medium == "email":
                            try:
                                address = canonicalise_email(address)
                            except ValueError as e:
                                raise SynapseError(400, str(e))

                        existing_user_id = await self.store.get_user_id_by_threepid(
                            medium, address
                        )

                        if existing_user_id is not None:
                            raise SynapseError(
                                400,
                                "%s is already in use" % medium,
                                Codes.THREEPID_IN_USE,
                            )

            entries = await self.store.get_user_agents_ips_to_ui_auth_session(
                session_id
            )

            display_name = await (
                self.password_auth_provider.get_displayname_for_registration(
                    auth_result, params
                )
            )

            registered_user_id = await self.registration_handler.register_user(
                localpart=desired_username,
                password_hash=password_hash,
                guest_access_token=guest_access_token,
                threepid=threepid,
                default_display_name=display_name,
                address=client_addr,
                user_agent_ips=entries,
            )
            # Necessary due to auth checks prior to the threepid being
            # written to the db
            if threepid:
                if is_threepid_reserved(
                    self.hs.config.server.mau_limits_reserved_threepids, threepid
                ):
                    await self.store.upsert_monthly_active_user(registered_user_id)

            # Remember that the user account has been registered (and the user
            # ID it was registered with, since it might not have been specified).
            await self.auth_handler.set_session_data(
                session_id,
                UIAuthSessionDataConstants.REGISTERED_USER_ID,
                registered_user_id,
            )

            registered = True

        return_dict = await self._create_registration_details(
            registered_user_id,
            params,
            should_issue_refresh_token=should_issue_refresh_token,
        )

        if registered:
            # Check if a token was used to authenticate registration
            registration_token = await self.auth_handler.get_session_data(
                session_id,
                UIAuthSessionDataConstants.REGISTRATION_TOKEN,
            )
            if registration_token:
                # Increment the `completed` counter for the token
                await self.store.use_registration_token(registration_token)
                # Indicate that the token has been successfully used so that
                # pending is not decremented again when expiring old UIA sessions.
                await self.store.mark_ui_auth_stage_complete(
                    session_id,
                    LoginType.REGISTRATION_TOKEN,
                    True,
                )

            await self.registration_handler.post_registration_actions(
                user_id=registered_user_id,
                auth_result=auth_result,
                access_token=return_dict.get("access_token"),
            )

            if self._require_approval:
                raise NotApprovedError(
                    msg="This account needs to be approved by an administrator before it can be used.",
                    approval_notice_medium=ApprovalNoticeMedium.NONE,
                )

        return 200, return_dict

    async def _do_appservice_registration(
        self,
        username: str,
        as_token: str,
        body: JsonDict,
        should_issue_refresh_token: bool = False,
    ) -> JsonDict:
        user_id, appservice = await self.registration_handler.appservice_register(
            username, as_token
        )
        if appservice.msc4190_device_management and not body.get("inhibit_login"):
            raise SynapseError(
                400,
                "This appservice has MSC4190 enabled, so the inhibit_login parameter must be set to true.",
                errcode=Codes.APPSERVICE_LOGIN_UNSUPPORTED,
            )

        return await self._create_registration_details(
            user_id,
            body,
            is_appservice_ghost=True,
            should_issue_refresh_token=should_issue_refresh_token,
        )

    async def _create_registration_details(
        self,
        user_id: str,
        params: JsonDict,
        is_appservice_ghost: bool = False,
        should_issue_refresh_token: bool = False,
    ) -> JsonDict:
        """Complete registration of newly-registered user

        Allocates device_id if one was not given; also creates access_token.

        Args:
            user_id: full canonical @user:id
            params: registration parameters, from which we pull device_id,
                initial_device_name and inhibit_login
            is_appservice_ghost
            should_issue_refresh_token: True if this registration should issue
                a refresh token alongside the access token.
        Returns:
             dictionary for response from /register
        """
        result: JsonDict = {
            "user_id": user_id,
            "home_server": self.hs.hostname,
        }
        # We don't want to log the user in if we're going to deny them access because
        # they need to be approved first.
        if not params.get("inhibit_login", False) and not self._require_approval:
            device_id = params.get("device_id")
            initial_display_name = params.get("initial_device_display_name")
            (
                device_id,
                access_token,
                valid_until_ms,
                refresh_token,
            ) = await self.registration_handler.register_device(
                user_id,
                device_id,
                initial_display_name,
                is_guest=False,
                is_appservice_ghost=is_appservice_ghost,
                should_issue_refresh_token=should_issue_refresh_token,
            )

            result.update({"access_token": access_token, "device_id": device_id})

            if valid_until_ms is not None:
                expires_in_ms = valid_until_ms - self.clock.time_msec()
                result["expires_in_ms"] = expires_in_ms

            if refresh_token is not None:
                result["refresh_token"] = refresh_token

        return result

    async def _do_guest_registration(
        self, params: JsonDict, address: str | None = None
    ) -> tuple[int, JsonDict]:
        if not self.hs.config.registration.allow_guest_access:
            raise SynapseError(403, "Guest access is disabled")
        user_id = await self.registration_handler.register_user(
            make_guest=True, address=address
        )

        # we don't allow guests to specify their own device_id, because
        # we have nowhere to store it.
        device_id = synapse.api.auth.GUEST_DEVICE_ID
        initial_display_name = params.get("initial_device_display_name")
        (
            device_id,
            access_token,
            valid_until_ms,
            refresh_token,
        ) = await self.registration_handler.register_device(
            user_id, device_id, initial_display_name, is_guest=True
        )

        result: JsonDict = {
            "user_id": user_id,
            "device_id": device_id,
            "access_token": access_token,
            "home_server": self.hs.hostname,
        }

        if valid_until_ms is not None:
            expires_in_ms = valid_until_ms - self.clock.time_msec()
            result["expires_in_ms"] = expires_in_ms

        if refresh_token is not None:
            result["refresh_token"] = refresh_token

        return 200, result


class RegisterAppServiceOnlyRestServlet(RestServlet):
    """An alternative registration API endpoint that only allows ASes to register

    This replaces the regular /register endpoint if MSC3861. There are two notable
    differences with the regular /register endpoint:
     - It only allows the `m.login.application_service` login type
     - It does not create a device or access token for the just-registered user

    Note that the exact behaviour of this endpoint is not yet finalised. It should be
    just good enough to make most ASes work.
    """

    PATTERNS = client_patterns("/register$")
    CATEGORY = "Registration/login requests"

    def __init__(self, hs: "HomeServer"):
        super().__init__()

        self.auth = hs.get_auth()
        self.registration_handler = hs.get_registration_handler()
        self.ratelimiter = hs.get_registration_ratelimiter()

    @interactive_auth_handler
    async def on_POST(self, request: SynapseRequest) -> tuple[int, JsonDict]:
        body = parse_json_object_from_request(request)

        client_addr = request.getClientAddress().host

        await self.ratelimiter.ratelimit(None, client_addr, update=False)

        # Allow only ASes to use this API.
        if body.get("type") != APP_SERVICE_REGISTRATION_TYPE:
            raise SynapseError(
                403,
                "Registration has been disabled. Only m.login.application_service registrations are allowed.",
                errcode=Codes.FORBIDDEN,
            )
        if not body.get("inhibit_login"):
            raise SynapseError(
                400,
                "This server uses OAuth2, so the inhibit_login parameter must be set to true for appservice registrations.",
                errcode=Codes.APPSERVICE_LOGIN_UNSUPPORTED,
            )

        kind = parse_string(request, "kind", default="user")

        if kind == "guest":
            raise SynapseError(403, "Guest access is disabled")
        elif kind != "user":
            raise UnrecognizedRequestError(
                f"Do not understand membership kind: {kind}",
            )

        # Pull out the provided username and do basic sanity checks early since
        # the auth layer will store these in sessions.
        desired_username = body.get("username")
        if not isinstance(desired_username, str) or len(desired_username) > 512:
            raise SynapseError(400, "Invalid username")

        if not self.auth.has_access_token(request):
            raise SynapseError(
                400,
                "Appservice token must be provided when using a type of m.login.application_service",
            )

        # XXX we should check that desired_username is valid. Currently
        # we give appservices carte blanche for any insanity in mxids,
        # because the IRC bridges rely on being able to register stupid
        # IDs.

        as_token = self.auth.get_access_token_from_request(request)

        user_id, _ = await self.registration_handler.appservice_register(
            desired_username, as_token
        )
        return 200, {"user_id": user_id}


def _calculate_registration_flows(
    config: HomeServerConfig, auth_handler: AuthHandler
) -> list[list[str]]:
    """Get a suitable flows list for registration

    Args:
        config: server configuration
        auth_handler: authorization handler

    Returns: a list of supported flows
    """
    # FIXME: need a better error than "no auth flow found" for scenarios
    # where we required 3PID for registration but the user didn't give one
    require_email = "email" in config.registration.registrations_require_3pid
    require_msisdn = "msisdn" in config.registration.registrations_require_3pid

    show_msisdn = True
    show_email = True

    if config.registration.disable_msisdn_registration:
        show_msisdn = False
        require_msisdn = False

    enabled_auth_types = auth_handler.get_enabled_auth_types()
    if LoginType.EMAIL_IDENTITY not in enabled_auth_types:
        show_email = False
        if require_email:
            raise ConfigError(
                "Configuration requires email address at registration, but email "
                "validation is not configured"
            )

    if LoginType.MSISDN not in enabled_auth_types:
        show_msisdn = False
        if require_msisdn:
            raise ConfigError(
                "Configuration requires msisdn at registration, but msisdn "
                "validation is not configured"
            )

    flows = []

    # only support 3PIDless registration if no 3PIDs are required
    if not require_email and not require_msisdn:
        # Add a dummy step here, otherwise if a client completes
        # recaptcha first we'll assume they were going for this flow
        # and complete the request, when they could have been trying to
        # complete one of the flows with email/msisdn auth.
        flows.append([LoginType.DUMMY])

    # only support the email-only flow if we don't require MSISDN 3PIDs
    if show_email and not require_msisdn:
        flows.append([LoginType.EMAIL_IDENTITY])

    # only support the MSISDN-only flow if we don't require email 3PIDs
    if show_msisdn and not require_email:
        flows.append([LoginType.MSISDN])

    if show_email and show_msisdn:
        # always let users provide both MSISDN & email
        flows.append([LoginType.MSISDN, LoginType.EMAIL_IDENTITY])

    # Add a flow that doesn't require any 3pids, if the config requests it.
    if config.registration.enable_registration_token_3pid_bypass:
        flows.append([LoginType.REGISTRATION_TOKEN])

    # Prepend m.login.terms to all flows if we're requiring consent
    if config.consent.user_consent_at_registration:
        for flow in flows:
            flow.insert(0, LoginType.TERMS)

    # Prepend recaptcha to all flows if we're requiring captcha
    if config.captcha.enable_registration_captcha:
        for flow in flows:
            flow.insert(0, LoginType.RECAPTCHA)

    # Prepend registration token to all flows if we're requiring a token
    if config.registration.registration_requires_token:
        for flow in flows:
            if LoginType.REGISTRATION_TOKEN not in flow:
                flow.insert(0, LoginType.REGISTRATION_TOKEN)

    return flows


def register_servlets(hs: "HomeServer", http_server: HttpServer) -> None:
    if hs.config.mas.enabled or hs.config.experimental.msc3861.enabled:
        RegisterAppServiceOnlyRestServlet(hs).register(http_server)
        return

    if hs.config.worker.worker_app is None:
        EmailRegisterRequestTokenRestServlet(hs).register(http_server)
        MsisdnRegisterRequestTokenRestServlet(hs).register(http_server)
        RegistrationSubmitTokenServlet(hs).register(http_server)
    UsernameAvailabilityRestServlet(hs).register(http_server)
    RegistrationTokenValidityRestServlet(hs).register(http_server)
    RegisterRestServlet(hs).register(http_server)
