MatrixSynapse/synapse/handlers/sso.py

# -*- coding: utf-8 -*-
# Copyright 2020 The Matrix.org Foundation C.I.C.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import logging
from typing import TYPE_CHECKING, Awaitable, Callable, List, Optional

import attr

from synapse.handlers._base import BaseHandler
from synapse.http.server import respond_with_html
from synapse.types import UserID, contains_invalid_mxid_characters

if TYPE_CHECKING:
    from synapse.server import HomeServer

logger = logging.getLogger(__name__)


class MappingException(Exception):
    """Used to catch errors when mapping the UserInfo object
    """


@attr.s
class UserAttributes:
    localpart = attr.ib(type=str)
    display_name = attr.ib(type=Optional[str], default=None)
    emails = attr.ib(type=List[str], default=attr.Factory(list))


class SsoHandler(BaseHandler):
    # The number of attempts to ask the mapping provider for when generating an MXID.
    _MAP_USERNAME_RETRIES = 1000

    def __init__(self, hs: "HomeServer"):
        super().__init__(hs)
        self._registration_handler = hs.get_registration_handler()
        self._error_template = hs.config.sso_error_template

    def render_error(
        self, request, error: str, error_description: Optional[str] = None
    ) -> None:
        """Renders the error template and responds with it.

        This is used to show errors to the user. The template of this page can
        be found under `synapse/res/templates/sso_error.html`.

        Args:
            request: The incoming request from the browser.
                We'll respond with an HTML page describing the error.
            error: A technical identifier for this error.
            error_description: A human-readable description of the error.
        """
        html = self._error_template.render(
            error=error, error_description=error_description
        )
        respond_with_html(request, 400, html)

    async def get_sso_user_by_remote_user_id(
        self, auth_provider_id: str, remote_user_id: str
    ) -> Optional[str]:
        """
        Maps the user ID of a remote IdP to a mxid for a previously seen user.

        If the user has not been seen yet, this will return None.

        Args:
            auth_provider_id: A unique identifier for this SSO provider, e.g.
                "oidc" or "saml".
            remote_user_id: The user ID according to the remote IdP. This might
                be an e-mail address, a GUID, or some other form. It must be
                unique and immutable.

        Returns:
            The mxid of a previously seen user.
        """
        logger.debug(
            "Looking for existing mapping for user %s:%s",
            auth_provider_id,
            remote_user_id,
        )

        # Check if we already have a mapping for this user.
        previously_registered_user_id = await self.store.get_user_by_external_id(
            auth_provider_id, remote_user_id,
        )

        # A match was found, return the user ID.
        if previously_registered_user_id is not None:
            logger.info(
                "Found existing mapping for IdP '%s' and remote_user_id '%s': %s",
                auth_provider_id,
                remote_user_id,
                previously_registered_user_id,
            )
            return previously_registered_user_id

        # No match.
        return None

    async def get_mxid_from_sso(
        self,
        auth_provider_id: str,
        remote_user_id: str,
        user_agent: str,
        ip_address: str,
        sso_to_matrix_id_mapper: Callable[[int], Awaitable[UserAttributes]],
        allow_existing_users: bool = False,
    ) -> str:
        """
        Given an SSO ID, retrieve the user ID for it and possibly register the user.

        This first checks if the SSO ID has previously been linked to a matrix ID,
        if it has that matrix ID is returned regardless of the current mapping
        logic.

        The mapping function is called (potentially multiple times) to generate
        a localpart for the user.

        If an unused localpart is generated, the user is registered from the
        given user-agent and IP address and the SSO ID is linked to this matrix
        ID for subsequent calls.

        If allow_existing_users is true the mapping function is only called once
        and results in:

            1. The use of a previously registered matrix ID. In this case, the
               SSO ID is linked to the matrix ID. (Note it is possible that
               other SSO IDs are linked to the same matrix ID.)
            2. An unused localpart, in which case the user is registered (as
               discussed above).
            3. An error if the generated localpart matches multiple pre-existing
               matrix IDs. Generally this should not happen.

        Args:
            auth_provider_id: A unique identifier for this SSO provider, e.g.
                "oidc" or "saml".
            remote_user_id: The unique identifier from the SSO provider.
            user_agent: The user agent of the client making the request.
            ip_address: The IP address of the client making the request.
            sso_to_matrix_id_mapper: A callable to generate the user attributes.
                The only parameter is an integer which represents the amount of
                times the returned mxid localpart mapping has failed.
            allow_existing_users: True if the localpart returned from the
                mapping provider can be linked to an existing matrix ID.

        Returns:
             The user ID associated with the SSO response.

        Raises:
            MappingException if there was a problem mapping the response to a user.
            RedirectException: some mapping providers may raise this if they need
                to redirect to an interstitial page.

        """
        # first of all, check if we already have a mapping for this user
        previously_registered_user_id = await self.get_sso_user_by_remote_user_id(
            auth_provider_id, remote_user_id,
        )
        if previously_registered_user_id:
            return previously_registered_user_id

        # Otherwise, generate a new user.
        for i in range(self._MAP_USERNAME_RETRIES):
            try:
                attributes = await sso_to_matrix_id_mapper(i)
            except Exception as e:
                raise MappingException(
                    "Could not extract user attributes from SSO response: " + str(e)
                )

            logger.debug(
                "Retrieved user attributes from user mapping provider: %r (attempt %d)",
                attributes,
                i,
            )

            if not attributes.localpart:
                raise MappingException(
                    "Error parsing SSO response: SSO mapping provider plugin "
                    "did not return a localpart value"
                )

            # Check if this mxid already exists
            user_id = UserID(attributes.localpart, self.server_name).to_string()
            users = await self.store.get_users_by_id_case_insensitive(user_id)
            # Note, if allow_existing_users is true then the loop is guaranteed
            # to end on the first iteration: either by matching an existing user,
            # raising an error, or registering a new user. See the docstring for
            # more in-depth an explanation.
            if users and allow_existing_users:
                # If an existing matrix ID is returned, then use it.
                if len(users) == 1:
                    previously_registered_user_id = next(iter(users))
                elif user_id in users:
                    previously_registered_user_id = user_id
                else:
                    # Do not attempt to continue generating Matrix IDs.
                    raise MappingException(
                        "Attempted to login as '{}' but it matches more than one user inexactly: {}".format(
                            user_id, users
                        )
                    )

                # Future logins should also match this user ID.
                await self.store.record_user_external_id(
                    auth_provider_id, remote_user_id, previously_registered_user_id
                )

                return previously_registered_user_id

            elif not users:
                # This mxid is free
                break
        else:
            # Unable to generate a username in 1000 iterations
            # Break and return error to the user
            raise MappingException(
                "Unable to generate a Matrix ID from the SSO response"
            )

        # Since the localpart is provided via a potentially untrusted module,
        # ensure the MXID is valid before registering.
        if contains_invalid_mxid_characters(attributes.localpart):
            raise MappingException("localpart is invalid: %s" % (attributes.localpart,))

        logger.debug("Mapped SSO user to local part %s", attributes.localpart)
        registered_user_id = await self._registration_handler.register_user(
            localpart=attributes.localpart,
            default_display_name=attributes.display_name,
            bind_emails=attributes.emails,
            user_agent_ips=[(user_agent, ip_address)],
        )

        await self.store.record_user_external_id(
            auth_provider_id, remote_user_id, registered_user_id
        )
        return registered_user_id