MatrixSynapse/synapse/handlers/cas_handler.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
import xml.etree.ElementTree as ET
from typing import AnyStr, Dict, Optional, Tuple

from six.moves import urllib

from twisted.web.client import PartialDownloadError

from synapse.api.errors import Codes, LoginError
from synapse.http.site import SynapseRequest
from synapse.types import UserID, map_username_to_mxid_localpart

logger = logging.getLogger(__name__)


class CasHandler:
    """
    Utility class for to handle the response from a CAS SSO service.

    Args:
        hs (synapse.server.HomeServer)
    """

    def __init__(self, hs):
        self._hostname = hs.hostname
        self._auth_handler = hs.get_auth_handler()
        self._registration_handler = hs.get_registration_handler()

        self._cas_server_url = hs.config.cas_server_url
        self._cas_service_url = hs.config.cas_service_url
        self._cas_displayname_attribute = hs.config.cas_displayname_attribute
        self._cas_required_attributes = hs.config.cas_required_attributes

        self._http_client = hs.get_proxied_http_client()

    def _build_service_param(self, client_redirect_url: AnyStr) -> str:
        return "%s%s?%s" % (
            self._cas_service_url,
            "/_matrix/client/r0/login/cas/ticket",
            urllib.parse.urlencode({"redirectUrl": client_redirect_url}),
        )

    async def _handle_cas_response(
        self, request: SynapseRequest, cas_response_body: str, client_redirect_url: str
    ) -> None:
        """
        Retrieves the user and display name from the CAS response and continues with the authentication.

        Args:
            request: The original client request.
            cas_response_body: The response from the CAS server.
            client_redirect_url: The URl to redirect the client to when
                everything is done.
        """
        user, attributes = self._parse_cas_response(cas_response_body)
        displayname = attributes.pop(self._cas_displayname_attribute, None)

        for required_attribute, required_value in self._cas_required_attributes.items():
            # If required attribute was not in CAS Response - Forbidden
            if required_attribute not in attributes:
                raise LoginError(401, "Unauthorized", errcode=Codes.UNAUTHORIZED)

            # Also need to check value
            if required_value is not None:
                actual_value = attributes[required_attribute]
                # If required attribute value does not match expected - Forbidden
                if required_value != actual_value:
                    raise LoginError(401, "Unauthorized", errcode=Codes.UNAUTHORIZED)

        await self._on_successful_auth(user, request, client_redirect_url, displayname)

    def _parse_cas_response(
        self, cas_response_body: str
    ) -> Tuple[str, Dict[str, Optional[str]]]:
        """
        Retrieve the user and other parameters from the CAS response.

        Args:
            cas_response_body: The response from the CAS query.

        Returns:
            A tuple of the user and a mapping of other attributes.
        """
        user = None
        attributes = {}
        try:
            root = ET.fromstring(cas_response_body)
            if not root.tag.endswith("serviceResponse"):
                raise Exception("root of CAS response is not serviceResponse")
            success = root[0].tag.endswith("authenticationSuccess")
            for child in root[0]:
                if child.tag.endswith("user"):
                    user = child.text
                if child.tag.endswith("attributes"):
                    for attribute in child:
                        # ElementTree library expands the namespace in
                        # attribute tags to the full URL of the namespace.
                        # We don't care about namespace here and it will always
                        # be encased in curly braces, so we remove them.
                        tag = attribute.tag
                        if "}" in tag:
                            tag = tag.split("}")[1]
                        attributes[tag] = attribute.text
            if user is None:
                raise Exception("CAS response does not contain user")
        except Exception:
            logger.exception("Error parsing CAS response")
            raise LoginError(401, "Invalid CAS response", errcode=Codes.UNAUTHORIZED)
        if not success:
            raise LoginError(
                401, "Unsuccessful CAS response", errcode=Codes.UNAUTHORIZED
            )
        return user, attributes

    async def _on_successful_auth(
        self,
        username: str,
        request: SynapseRequest,
        client_redirect_url: str,
        user_display_name: Optional[str] = None,
    ) -> None:
        """Called once the user has successfully authenticated with the SSO.

        Registers the user if necessary, and then returns a redirect (with
        a login token) to the client.

        Args:
            username: the remote user id. We'll map this onto
                something sane for a MXID localpath.

            request: the incoming request from the browser. We'll
                respond to it with a redirect.

            client_redirect_url: the redirect_url the client gave us when
                it first started the process.

            user_display_name: if set, and we have to register a new user,
                we will set their displayname to this.
        """
        localpart = map_username_to_mxid_localpart(username)
        user_id = UserID(localpart, self._hostname).to_string()
        registered_user_id = await self._auth_handler.check_user_exists(user_id)
        if not registered_user_id:
            registered_user_id = await self._registration_handler.register_user(
                localpart=localpart, default_display_name=user_display_name
            )

        self._auth_handler.complete_sso_login(
            registered_user_id, request, client_redirect_url
        )

    def handle_redirect_request(self, client_redirect_url: bytes) -> bytes:
        """
        Generates a URL to the CAS server where the client should be redirected.

        Args:
            client_redirect_url: The final URL the client should go to after the
                user has negotiated SSO.

        Returns:
            The URL to redirect to.
        """
        args = urllib.parse.urlencode(
            {"service": self._build_service_param(client_redirect_url)}
        )

        return ("%s/login?%s" % (self._cas_server_url, args)).encode("ascii")

    async def handle_ticket_request(
        self, request: SynapseRequest, client_redirect_url: str, ticket: str
    ) -> None:
        """
        Validates a CAS ticket sent by the client for login/registration.

        On a successful request, writes a redirect to the request.
        """
        uri = self._cas_server_url + "/proxyValidate"
        args = {
            "ticket": ticket,
            "service": self._build_service_param(client_redirect_url),
        }
        try:
            body = await self._http_client.get_raw(uri, args)
        except PartialDownloadError as pde:
            # Twisted raises this error if the connection is closed,
            # even if that's being used old-http style to signal end-of-data
            body = pde.response

        await self._handle_cas_response(request, body, client_redirect_url)