MatrixSynapse/synapse/handlers/identity.py

# -*- coding: utf-8 -*-
# Copyright 2015, 2016 OpenMarket Ltd
# Copyright 2017 Vector Creations Ltd
# Copyright 2018 New Vector 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.

"""Utilities for interacting with Identity Servers"""

import logging
import urllib.parse
from typing import Awaitable, Callable, Dict, List, Optional, Tuple

from canonicaljson import json

from twisted.internet.error import TimeoutError

from synapse.api.errors import (
    CodeMessageException,
    Codes,
    HttpResponseException,
    SynapseError,
)
from synapse.config.emailconfig import ThreepidBehaviour
from synapse.http.client import SimpleHttpClient
from synapse.types import JsonDict, Requester
from synapse.util.hash import sha256_and_url_safe_base64
from synapse.util.stringutils import assert_valid_client_secret, random_string

from ._base import BaseHandler

logger = logging.getLogger(__name__)

id_server_scheme = "https://"


class IdentityHandler(BaseHandler):
    def __init__(self, hs):
        super(IdentityHandler, self).__init__(hs)

        self.http_client = SimpleHttpClient(hs)
        # We create a blacklisting instance of SimpleHttpClient for contacting identity
        # servers specified by clients
        self.blacklisting_http_client = SimpleHttpClient(
            hs, ip_blacklist=hs.config.federation_ip_range_blacklist
        )
        self.federation_http_client = hs.get_http_client()
        self.hs = hs

    async def threepid_from_creds(
        self, id_server: str, creds: Dict[str, str]
    ) -> Optional[JsonDict]:
        """
        Retrieve and validate a threepid identifier from a "credentials" dictionary against a
        given identity server

        Args:
            id_server: The identity server to validate 3PIDs against. Must be a
                complete URL including the protocol (http(s)://)
            creds: Dictionary containing the following keys:
                * client_secret|clientSecret: A unique secret str provided by the client
                * sid: The ID of the validation session

        Returns:
            A dictionary consisting of response params to the /getValidated3pid
            endpoint of the Identity Service API, or None if the threepid was not found
        """
        client_secret = creds.get("client_secret") or creds.get("clientSecret")
        if not client_secret:
            raise SynapseError(
                400, "Missing param client_secret in creds", errcode=Codes.MISSING_PARAM
            )
        assert_valid_client_secret(client_secret)

        session_id = creds.get("sid")
        if not session_id:
            raise SynapseError(
                400, "Missing param session_id in creds", errcode=Codes.MISSING_PARAM
            )

        query_params = {"sid": session_id, "client_secret": client_secret}

        url = id_server + "/_matrix/identity/api/v1/3pid/getValidated3pid"

        try:
            data = await self.http_client.get_json(url, query_params)
        except TimeoutError:
            raise SynapseError(500, "Timed out contacting identity server")
        except HttpResponseException as e:
            logger.info(
                "%s returned %i for threepid validation for: %s",
                id_server,
                e.code,
                creds,
            )
            return None

        # Old versions of Sydent return a 200 http code even on a failed validation
        # check. Thus, in addition to the HttpResponseException check above (which
        # checks for non-200 errors), we need to make sure validation_session isn't
        # actually an error, identified by the absence of a "medium" key
        # See https://github.com/matrix-org/sydent/issues/215 for details
        if "medium" in data:
            return data

        logger.info("%s reported non-validated threepid: %s", id_server, creds)
        return None

    async def bind_threepid(
        self,
        client_secret: str,
        sid: str,
        mxid: str,
        id_server: str,
        id_access_token: Optional[str] = None,
        use_v2: bool = True,
    ) -> JsonDict:
        """Bind a 3PID to an identity server

        Args:
            client_secret: A unique secret provided by the client
            sid: The ID of the validation session
            mxid: The MXID to bind the 3PID to
            id_server: The domain of the identity server to query
            id_access_token: The access token to authenticate to the identity
                server with, if necessary. Required if use_v2 is true
            use_v2: Whether to use v2 Identity Service API endpoints. Defaults to True

        Returns:
            The response from the identity server
        """
        logger.debug("Proxying threepid bind request for %s to %s", mxid, id_server)

        # If an id_access_token is not supplied, force usage of v1
        if id_access_token is None:
            use_v2 = False

        # Decide which API endpoint URLs to use
        headers = {}
        bind_data = {"sid": sid, "client_secret": client_secret, "mxid": mxid}
        if use_v2:
            bind_url = "https://%s/_matrix/identity/v2/3pid/bind" % (id_server,)
            headers["Authorization"] = create_id_access_token_header(id_access_token)  # type: ignore
        else:
            bind_url = "https://%s/_matrix/identity/api/v1/3pid/bind" % (id_server,)

        try:
            # Use the blacklisting http client as this call is only to identity servers
            # provided by a client
            data = await self.blacklisting_http_client.post_json_get_json(
                bind_url, bind_data, headers=headers
            )

            # Remember where we bound the threepid
            await self.store.add_user_bound_threepid(
                user_id=mxid,
                medium=data["medium"],
                address=data["address"],
                id_server=id_server,
            )

            return data
        except HttpResponseException as e:
            if e.code != 404 or not use_v2:
                logger.error("3PID bind failed with Matrix error: %r", e)
                raise e.to_synapse_error()
        except TimeoutError:
            raise SynapseError(500, "Timed out contacting identity server")
        except CodeMessageException as e:
            data = json.loads(e.msg)  # XXX WAT?
            return data

        logger.info("Got 404 when POSTing JSON %s, falling back to v1 URL", bind_url)
        res = await self.bind_threepid(
            client_secret, sid, mxid, id_server, id_access_token, use_v2=False
        )
        return res

    async def try_unbind_threepid(self, mxid: str, threepid: dict) -> bool:
        """Attempt to remove a 3PID from an identity server, or if one is not provided, all
        identity servers we're aware the binding is present on

        Args:
            mxid: Matrix user ID of binding to be removed
            threepid: Dict with medium & address of binding to be
                removed, and an optional id_server.

        Raises:
            SynapseError: If we failed to contact the identity server

        Returns:
            True on success, otherwise False if the identity
            server doesn't support unbinding (or no identity server found to
            contact).
        """
        if threepid.get("id_server"):
            id_servers = [threepid["id_server"]]
        else:
            id_servers = await self.store.get_id_servers_user_bound(
                user_id=mxid, medium=threepid["medium"], address=threepid["address"]
            )

        # We don't know where to unbind, so we don't have a choice but to return
        if not id_servers:
            return False

        changed = True
        for id_server in id_servers:
            changed &= await self.try_unbind_threepid_with_id_server(
                mxid, threepid, id_server
            )

        return changed

    async def try_unbind_threepid_with_id_server(
        self, mxid: str, threepid: dict, id_server: str
    ) -> bool:
        """Removes a binding from an identity server

        Args:
            mxid: Matrix user ID of binding to be removed
            threepid: Dict with medium & address of binding to be removed
            id_server: Identity server to unbind from

        Raises:
            SynapseError: If we failed to contact the identity server

        Returns:
            True on success, otherwise False if the identity
            server doesn't support unbinding
        """
        url = "https://%s/_matrix/identity/api/v1/3pid/unbind" % (id_server,)
        url_bytes = "/_matrix/identity/api/v1/3pid/unbind".encode("ascii")

        content = {
            "mxid": mxid,
            "threepid": {"medium": threepid["medium"], "address": threepid["address"]},
        }

        # we abuse the federation http client to sign the request, but we have to send it
        # using the normal http client since we don't want the SRV lookup and want normal
        # 'browser-like' HTTPS.
        auth_headers = self.federation_http_client.build_auth_headers(
            destination=None,
            method=b"POST",
            url_bytes=url_bytes,
            content=content,
            destination_is=id_server.encode("ascii"),
        )
        headers = {b"Authorization": auth_headers}

        try:
            # Use the blacklisting http client as this call is only to identity servers
            # provided by a client
            await self.blacklisting_http_client.post_json_get_json(
                url, content, headers
            )
            changed = True
        except HttpResponseException as e:
            changed = False
            if e.code in (400, 404, 501):
                # The remote server probably doesn't support unbinding (yet)
                logger.warning("Received %d response while unbinding threepid", e.code)
            else:
                logger.error("Failed to unbind threepid on identity server: %s", e)
                raise SynapseError(500, "Failed to contact identity server")
        except TimeoutError:
            raise SynapseError(500, "Timed out contacting identity server")

        await self.store.remove_user_bound_threepid(
            user_id=mxid,
            medium=threepid["medium"],
            address=threepid["address"],
            id_server=id_server,
        )

        return changed

    async def send_threepid_validation(
        self,
        email_address: str,
        client_secret: str,
        send_attempt: int,
        send_email_func: Callable[[str, str, str, str], Awaitable],
        next_link: Optional[str] = None,
    ) -> str:
        """Send a threepid validation email for password reset or
        registration purposes

        Args:
            email_address: The user's email address
            client_secret: The provided client secret
            send_attempt: Which send attempt this is
            send_email_func: A function that takes an email address, token,
                             client_secret and session_id, sends an email
                             and returns an Awaitable.
            next_link: The URL to redirect the user to after validation

        Returns:
            The new session_id upon success

        Raises:
            SynapseError is an error occurred when sending the email
        """
        # Check that this email/client_secret/send_attempt combo is new or
        # greater than what we've seen previously
        session = await self.store.get_threepid_validation_session(
            "email", client_secret, address=email_address, validated=False
        )

        # Check to see if a session already exists and that it is not yet
        # marked as validated
        if session and session.get("validated_at") is None:
            session_id = session["session_id"]
            last_send_attempt = session["last_send_attempt"]

            # Check that the send_attempt is higher than previous attempts
            if send_attempt <= last_send_attempt:
                # If not, just return a success without sending an email
                return session_id
        else:
            # An non-validated session does not exist yet.
            # Generate a session id
            session_id = random_string(16)

        if next_link:
            # Manipulate the next_link to add the sid, because the caller won't get
            # it until we send a response, by which time we've sent the mail.
            if "?" in next_link:
                next_link += "&"
            else:
                next_link += "?"
            next_link += "sid=" + urllib.parse.quote(session_id)

        # Generate a new validation token
        token = random_string(32)

        # Send the mail with the link containing the token, client_secret
        # and session_id
        try:
            await send_email_func(email_address, token, client_secret, session_id)
        except Exception:
            logger.exception(
                "Error sending threepid validation email to %s", email_address
            )
            raise SynapseError(500, "An error was encountered when sending the email")

        token_expires = (
            self.hs.clock.time_msec() + self.hs.config.email_validation_token_lifetime
        )

        await self.store.start_or_continue_validation_session(
            "email",
            email_address,
            session_id,
            client_secret,
            send_attempt,
            next_link,
            token,
            token_expires,
        )

        return session_id

    async def requestEmailToken(
        self,
        id_server: str,
        email: str,
        client_secret: str,
        send_attempt: int,
        next_link: Optional[str] = None,
    ) -> JsonDict:
        """
        Request an external server send an email on our behalf for the purposes of threepid
        validation.

        Args:
            id_server: The identity server to proxy to
            email: The email to send the message to
            client_secret: The unique client_secret sends by the user
            send_attempt: Which attempt this is
            next_link: A link to redirect the user to once they submit the token

        Returns:
            The json response body from the server
        """
        params = {
            "email": email,
            "client_secret": client_secret,
            "send_attempt": send_attempt,
        }
        if next_link:
            params["next_link"] = next_link

        if self.hs.config.using_identity_server_from_trusted_list:
            # Warn that a deprecated config option is in use
            logger.warning(
                'The config option "trust_identity_server_for_password_resets" '
                'has been replaced by "account_threepid_delegate". '
                "Please consult the sample config at docs/sample_config.yaml for "
                "details and update your config file."
            )

        try:
            data = await self.http_client.post_json_get_json(
                id_server + "/_matrix/identity/api/v1/validate/email/requestToken",
                params,
            )
            return data
        except HttpResponseException as e:
            logger.info("Proxied requestToken failed: %r", e)
            raise e.to_synapse_error()
        except TimeoutError:
            raise SynapseError(500, "Timed out contacting identity server")

    async def requestMsisdnToken(
        self,
        id_server: str,
        country: str,
        phone_number: str,
        client_secret: str,
        send_attempt: int,
        next_link: Optional[str] = None,
    ) -> JsonDict:
        """
        Request an external server send an SMS message on our behalf for the purposes of
        threepid validation.
        Args:
            id_server: The identity server to proxy to
            country: The country code of the phone number
            phone_number: The number to send the message to
            client_secret: The unique client_secret sends by the user
            send_attempt: Which attempt this is
            next_link: A link to redirect the user to once they submit the token

        Returns:
            The json response body from the server
        """
        params = {
            "country": country,
            "phone_number": phone_number,
            "client_secret": client_secret,
            "send_attempt": send_attempt,
        }
        if next_link:
            params["next_link"] = next_link

        if self.hs.config.using_identity_server_from_trusted_list:
            # Warn that a deprecated config option is in use
            logger.warning(
                'The config option "trust_identity_server_for_password_resets" '
                'has been replaced by "account_threepid_delegate". '
                "Please consult the sample config at docs/sample_config.yaml for "
                "details and update your config file."
            )

        try:
            data = await self.http_client.post_json_get_json(
                id_server + "/_matrix/identity/api/v1/validate/msisdn/requestToken",
                params,
            )
        except HttpResponseException as e:
            logger.info("Proxied requestToken failed: %r", e)
            raise e.to_synapse_error()
        except TimeoutError:
            raise SynapseError(500, "Timed out contacting identity server")

        assert self.hs.config.public_baseurl

        # we need to tell the client to send the token back to us, since it doesn't
        # otherwise know where to send it, so add submit_url response parameter
        # (see also MSC2078)
        data["submit_url"] = (
            self.hs.config.public_baseurl
            + "_matrix/client/unstable/add_threepid/msisdn/submit_token"
        )
        return data

    async def validate_threepid_session(
        self, client_secret: str, sid: str
    ) -> Optional[JsonDict]:
        """Validates a threepid session with only the client secret and session ID
        Tries validating against any configured account_threepid_delegates as well as locally.

        Args:
            client_secret: A secret provided by the client
            sid: The ID of the session

        Returns:
            The json response if validation was successful, otherwise None
        """
        # XXX: We shouldn't need to keep wrapping and unwrapping this value
        threepid_creds = {"client_secret": client_secret, "sid": sid}

        # We don't actually know which medium this 3PID is. Thus we first assume it's email,
        # and if validation fails we try msisdn
        validation_session = None

        # Try to validate as email
        if self.hs.config.threepid_behaviour_email == ThreepidBehaviour.REMOTE:
            # Ask our delegated email identity server
            validation_session = await self.threepid_from_creds(
                self.hs.config.account_threepid_delegate_email, threepid_creds
            )
        elif self.hs.config.threepid_behaviour_email == ThreepidBehaviour.LOCAL:
            # Get a validated session matching these details
            validation_session = await self.store.get_threepid_validation_session(
                "email", client_secret, sid=sid, validated=True
            )

        if validation_session:
            return validation_session

        # Try to validate as msisdn
        if self.hs.config.account_threepid_delegate_msisdn:
            # Ask our delegated msisdn identity server
            validation_session = await self.threepid_from_creds(
                self.hs.config.account_threepid_delegate_msisdn, threepid_creds
            )

        return validation_session

    async def proxy_msisdn_submit_token(
        self, id_server: str, client_secret: str, sid: str, token: str
    ) -> JsonDict:
        """Proxy a POST submitToken request to an identity server for verification purposes

        Args:
            id_server: The identity server URL to contact
            client_secret: Secret provided by the client
            sid: The ID of the session
            token: The verification token

        Raises:
            SynapseError: If we failed to contact the identity server

        Returns:
            The response dict from the identity server
        """
        body = {"client_secret": client_secret, "sid": sid, "token": token}

        try:
            return await self.http_client.post_json_get_json(
                id_server + "/_matrix/identity/api/v1/validate/msisdn/submitToken",
                body,
            )
        except TimeoutError:
            raise SynapseError(500, "Timed out contacting identity server")
        except HttpResponseException as e:
            logger.warning("Error contacting msisdn account_threepid_delegate: %s", e)
            raise SynapseError(400, "Error contacting the identity server")

    async def lookup_3pid(
        self,
        id_server: str,
        medium: str,
        address: str,
        id_access_token: Optional[str] = None,
    ) -> Optional[str]:
        """Looks up a 3pid in the passed identity server.

        Args:
            id_server: The server name (including port, if required)
                of the identity server to use.
            medium: The type of the third party identifier (e.g. "email").
            address: The third party identifier (e.g. "foo@example.com").
            id_access_token: The access token to authenticate to the identity
                server with

        Returns:
            the matrix ID of the 3pid, or None if it is not recognized.
        """
        if id_access_token is not None:
            try:
                results = await self._lookup_3pid_v2(
                    id_server, id_access_token, medium, address
                )
                return results

            except Exception as e:
                # Catch HttpResponseExcept for a non-200 response code
                # Check if this identity server does not know about v2 lookups
                if isinstance(e, HttpResponseException) and e.code == 404:
                    # This is an old identity server that does not yet support v2 lookups
                    logger.warning(
                        "Attempted v2 lookup on v1 identity server %s. Falling "
                        "back to v1",
                        id_server,
                    )
                else:
                    logger.warning("Error when looking up hashing details: %s", e)
                    return None

        return await self._lookup_3pid_v1(id_server, medium, address)

    async def _lookup_3pid_v1(
        self, id_server: str, medium: str, address: str
    ) -> Optional[str]:
        """Looks up a 3pid in the passed identity server using v1 lookup.

        Args:
            id_server: The server name (including port, if required)
                of the identity server to use.
            medium: The type of the third party identifier (e.g. "email").
            address: The third party identifier (e.g. "foo@example.com").

        Returns:
            the matrix ID of the 3pid, or None if it is not recognized.
        """
        try:
            data = await self.blacklisting_http_client.get_json(
                "%s%s/_matrix/identity/api/v1/lookup" % (id_server_scheme, id_server),
                {"medium": medium, "address": address},
            )

            if "mxid" in data:
                # note: we used to verify the identity server's signature here, but no longer
                # require or validate it. See the following for context:
                # https://github.com/matrix-org/synapse/issues/5253#issuecomment-666246950
                return data["mxid"]
        except TimeoutError:
            raise SynapseError(500, "Timed out contacting identity server")
        except IOError as e:
            logger.warning("Error from v1 identity server lookup: %s" % (e,))

        return None

    async def _lookup_3pid_v2(
        self, id_server: str, id_access_token: str, medium: str, address: str
    ) -> Optional[str]:
        """Looks up a 3pid in the passed identity server using v2 lookup.

        Args:
            id_server: The server name (including port, if required)
                of the identity server to use.
            id_access_token: The access token to authenticate to the identity server with
            medium: The type of the third party identifier (e.g. "email").
            address: The third party identifier (e.g. "foo@example.com").

        Returns:
            the matrix ID of the 3pid, or None if it is not recognised.
        """
        # Check what hashing details are supported by this identity server
        try:
            hash_details = await self.blacklisting_http_client.get_json(
                "%s%s/_matrix/identity/v2/hash_details" % (id_server_scheme, id_server),
                {"access_token": id_access_token},
            )
        except TimeoutError:
            raise SynapseError(500, "Timed out contacting identity server")

        if not isinstance(hash_details, dict):
            logger.warning(
                "Got non-dict object when checking hash details of %s%s: %s",
                id_server_scheme,
                id_server,
                hash_details,
            )
            raise SynapseError(
                400,
                "Non-dict object from %s%s during v2 hash_details request: %s"
                % (id_server_scheme, id_server, hash_details),
            )

        # Extract information from hash_details
        supported_lookup_algorithms = hash_details.get("algorithms")
        lookup_pepper = hash_details.get("lookup_pepper")
        if (
            not supported_lookup_algorithms
            or not isinstance(supported_lookup_algorithms, list)
            or not lookup_pepper
            or not isinstance(lookup_pepper, str)
        ):
            raise SynapseError(
                400,
                "Invalid hash details received from identity server %s%s: %s"
                % (id_server_scheme, id_server, hash_details),
            )

        # Check if any of the supported lookup algorithms are present
        if LookupAlgorithm.SHA256 in supported_lookup_algorithms:
            # Perform a hashed lookup
            lookup_algorithm = LookupAlgorithm.SHA256

            # Hash address, medium and the pepper with sha256
            to_hash = "%s %s %s" % (address, medium, lookup_pepper)
            lookup_value = sha256_and_url_safe_base64(to_hash)

        elif LookupAlgorithm.NONE in supported_lookup_algorithms:
            # Perform a non-hashed lookup
            lookup_algorithm = LookupAlgorithm.NONE

            # Combine together plaintext address and medium
            lookup_value = "%s %s" % (address, medium)

        else:
            logger.warning(
                "None of the provided lookup algorithms of %s are supported: %s",
                id_server,
                supported_lookup_algorithms,
            )
            raise SynapseError(
                400,
                "Provided identity server does not support any v2 lookup "
                "algorithms that this homeserver supports.",
            )

        # Authenticate with identity server given the access token from the client
        headers = {"Authorization": create_id_access_token_header(id_access_token)}

        try:
            lookup_results = await self.blacklisting_http_client.post_json_get_json(
                "%s%s/_matrix/identity/v2/lookup" % (id_server_scheme, id_server),
                {
                    "addresses": [lookup_value],
                    "algorithm": lookup_algorithm,
                    "pepper": lookup_pepper,
                },
                headers=headers,
            )
        except TimeoutError:
            raise SynapseError(500, "Timed out contacting identity server")
        except Exception as e:
            logger.warning("Error when performing a v2 3pid lookup: %s", e)
            raise SynapseError(
                500, "Unknown error occurred during identity server lookup"
            )

        # Check for a mapping from what we looked up to an MXID
        if "mappings" not in lookup_results or not isinstance(
            lookup_results["mappings"], dict
        ):
            logger.warning("No results from 3pid lookup")
            return None

        # Return the MXID if it's available, or None otherwise
        mxid = lookup_results["mappings"].get(lookup_value)
        return mxid

    async def ask_id_server_for_third_party_invite(
        self,
        requester: Requester,
        id_server: str,
        medium: str,
        address: str,
        room_id: str,
        inviter_user_id: str,
        room_alias: str,
        room_avatar_url: str,
        room_join_rules: str,
        room_name: str,
        inviter_display_name: str,
        inviter_avatar_url: str,
        id_access_token: Optional[str] = None,
    ) -> Tuple[str, List[Dict[str, str]], Dict[str, str], str]:
        """
        Asks an identity server for a third party invite.

        Args:
            requester
            id_server: hostname + optional port for the identity server.
            medium: The literal string "email".
            address: The third party address being invited.
            room_id: The ID of the room to which the user is invited.
            inviter_user_id: The user ID of the inviter.
            room_alias: An alias for the room, for cosmetic notifications.
            room_avatar_url: The URL of the room's avatar, for cosmetic
                notifications.
            room_join_rules: The join rules of the email (e.g. "public").
            room_name: The m.room.name of the room.
            inviter_display_name: The current display name of the
                inviter.
            inviter_avatar_url: The URL of the inviter's avatar.
            id_access_token (str|None): The access token to authenticate to the identity
                server with

        Returns:
            A tuple containing:
                token: The token which must be signed to prove authenticity.
                public_keys ([{"public_key": str, "key_validity_url": str}]):
                    public_key is a base64-encoded ed25519 public key.
                fallback_public_key: One element from public_keys.
                display_name: A user-friendly name to represent the invited user.
        """
        invite_config = {
            "medium": medium,
            "address": address,
            "room_id": room_id,
            "room_alias": room_alias,
            "room_avatar_url": room_avatar_url,
            "room_join_rules": room_join_rules,
            "room_name": room_name,
            "sender": inviter_user_id,
            "sender_display_name": inviter_display_name,
            "sender_avatar_url": inviter_avatar_url,
        }

        # Add the identity service access token to the JSON body and use the v2
        # Identity Service endpoints if id_access_token is present
        data = None
        base_url = "%s%s/_matrix/identity" % (id_server_scheme, id_server)

        if id_access_token:
            key_validity_url = "%s%s/_matrix/identity/v2/pubkey/isvalid" % (
                id_server_scheme,
                id_server,
            )

            # Attempt a v2 lookup
            url = base_url + "/v2/store-invite"
            try:
                data = await self.blacklisting_http_client.post_json_get_json(
                    url,
                    invite_config,
                    {"Authorization": create_id_access_token_header(id_access_token)},
                )
            except TimeoutError:
                raise SynapseError(500, "Timed out contacting identity server")
            except HttpResponseException as e:
                if e.code != 404:
                    logger.info("Failed to POST %s with JSON: %s", url, e)
                    raise e

        if data is None:
            key_validity_url = "%s%s/_matrix/identity/api/v1/pubkey/isvalid" % (
                id_server_scheme,
                id_server,
            )
            url = base_url + "/api/v1/store-invite"

            try:
                data = await self.blacklisting_http_client.post_json_get_json(
                    url, invite_config
                )
            except TimeoutError:
                raise SynapseError(500, "Timed out contacting identity server")
            except HttpResponseException as e:
                logger.warning(
                    "Error trying to call /store-invite on %s%s: %s",
                    id_server_scheme,
                    id_server,
                    e,
                )

            if data is None:
                # Some identity servers may only support application/x-www-form-urlencoded
                # types. This is especially true with old instances of Sydent, see
                # https://github.com/matrix-org/sydent/pull/170
                try:
                    data = await self.blacklisting_http_client.post_urlencoded_get_json(
                        url, invite_config
                    )
                except HttpResponseException as e:
                    logger.warning(
                        "Error calling /store-invite on %s%s with fallback "
                        "encoding: %s",
                        id_server_scheme,
                        id_server,
                        e,
                    )
                    raise e

        # TODO: Check for success
        token = data["token"]
        public_keys = data.get("public_keys", [])
        if "public_key" in data:
            fallback_public_key = {
                "public_key": data["public_key"],
                "key_validity_url": key_validity_url,
            }
        else:
            fallback_public_key = public_keys[0]

        if not public_keys:
            public_keys.append(fallback_public_key)
        display_name = data["display_name"]
        return token, public_keys, fallback_public_key, display_name


def create_id_access_token_header(id_access_token: str) -> List[str]:
    """Create an Authorization header for passing to SimpleHttpClient as the header value
    of an HTTP request.

    Args:
        id_access_token: An identity server access token.

    Returns:
        The ascii-encoded bearer token encased in a list.
    """
    # Prefix with Bearer
    bearer_token = "Bearer %s" % id_access_token

    # Encode headers to standard ascii
    bearer_token.encode("ascii")

    # Return as a list as that's how SimpleHttpClient takes header values
    return [bearer_token]


class LookupAlgorithm:
    """
    Supported hashing algorithms when performing a 3PID lookup.

    SHA256 - Hashing an (address, medium, pepper) combo with sha256, then url-safe base64
        encoding
    NONE - Not performing any hashing. Simply sending an (address, medium) combo in plaintext
    """

    SHA256 = "sha256"
    NONE = "none"