394 lines
14 KiB
Python
394 lines
14 KiB
Python
# Copyright 2020 The Matrix.org Foundation C.I.C.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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import logging
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import urllib.parse
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from typing import TYPE_CHECKING, Dict, List, Optional
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from xml.etree import ElementTree as ET
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import attr
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from twisted.web.client import PartialDownloadError
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from synapse.api.errors import HttpResponseException
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from synapse.handlers.sso import MappingException, UserAttributes
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from synapse.http.site import SynapseRequest
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from synapse.types import UserID, map_username_to_mxid_localpart
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if TYPE_CHECKING:
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from synapse.server import HomeServer
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logger = logging.getLogger(__name__)
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class CasError(Exception):
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"""Used to catch errors when validating the CAS ticket."""
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def __init__(self, error: str, error_description: Optional[str] = None):
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self.error = error
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self.error_description = error_description
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def __str__(self) -> str:
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if self.error_description:
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return f"{self.error}: {self.error_description}"
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return self.error
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@attr.s(slots=True, frozen=True, auto_attribs=True)
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class CasResponse:
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username: str
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attributes: Dict[str, List[Optional[str]]]
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class CasHandler:
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"""
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Utility class for to handle the response from a CAS SSO service.
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Args:
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hs
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"""
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def __init__(self, hs: "HomeServer"):
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self.hs = hs
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self._hostname = hs.hostname
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self._store = hs.get_datastores().main
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self._auth_handler = hs.get_auth_handler()
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self._registration_handler = hs.get_registration_handler()
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self._cas_server_url = hs.config.cas.cas_server_url
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self._cas_service_url = hs.config.cas.cas_service_url
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self._cas_displayname_attribute = hs.config.cas.cas_displayname_attribute
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self._cas_required_attributes = hs.config.cas.cas_required_attributes
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self._http_client = hs.get_proxied_http_client()
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# identifier for the external_ids table
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self.idp_id = "cas"
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# user-facing name of this auth provider
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self.idp_name = "CAS"
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# we do not currently support brands/icons for CAS auth, but this is required by
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# the SsoIdentityProvider protocol type.
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self.idp_icon = None
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self.idp_brand = None
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self._sso_handler = hs.get_sso_handler()
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self._sso_handler.register_identity_provider(self)
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def _build_service_param(self, args: Dict[str, str]) -> str:
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"""
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Generates a value to use as the "service" parameter when redirecting or
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querying the CAS service.
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Args:
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args: Additional arguments to include in the final redirect URL.
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Returns:
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The URL to use as a "service" parameter.
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"""
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return "%s?%s" % (
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self._cas_service_url,
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urllib.parse.urlencode(args),
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)
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async def _validate_ticket(
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self, ticket: str, service_args: Dict[str, str]
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) -> CasResponse:
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"""
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Validate a CAS ticket with the server, and return the parsed the response.
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Args:
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ticket: The CAS ticket from the client.
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service_args: Additional arguments to include in the service URL.
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Should be the same as those passed to `handle_redirect_request`.
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Raises:
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CasError: If there's an error parsing the CAS response.
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Returns:
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The parsed CAS response.
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"""
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uri = self._cas_server_url + "/proxyValidate"
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args = {
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"ticket": ticket,
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"service": self._build_service_param(service_args),
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}
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try:
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body = await self._http_client.get_raw(uri, args)
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except PartialDownloadError as pde:
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# Twisted raises this error if the connection is closed,
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# even if that's being used old-http style to signal end-of-data
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# Assertion is for mypy's benefit. Error.response is Optional[bytes],
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# but a PartialDownloadError should always have a non-None response.
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assert pde.response is not None
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body = pde.response
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except HttpResponseException as e:
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description = (
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'Authorization server responded with a "{status}" error '
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"while exchanging the authorization code."
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).format(status=e.code)
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raise CasError("server_error", description) from e
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return self._parse_cas_response(body)
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def _parse_cas_response(self, cas_response_body: bytes) -> CasResponse:
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"""
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Retrieve the user and other parameters from the CAS response.
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Args:
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cas_response_body: The response from the CAS query.
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Raises:
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CasError: If there's an error parsing the CAS response.
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Returns:
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The parsed CAS response.
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"""
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# Ensure the response is valid.
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root = ET.fromstring(cas_response_body)
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if not root.tag.endswith("serviceResponse"):
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raise CasError(
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"missing_service_response",
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"root of CAS response is not serviceResponse",
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)
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success = root[0].tag.endswith("authenticationSuccess")
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if not success:
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raise CasError("unsucessful_response", "Unsuccessful CAS response")
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# Iterate through the nodes and pull out the user and any extra attributes.
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user = None
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attributes: Dict[str, List[Optional[str]]] = {}
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for child in root[0]:
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if child.tag.endswith("user"):
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user = child.text
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if child.tag.endswith("attributes"):
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for attribute in child:
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# ElementTree library expands the namespace in
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# attribute tags to the full URL of the namespace.
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# We don't care about namespace here and it will always
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# be encased in curly braces, so we remove them.
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tag = attribute.tag
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if "}" in tag:
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tag = tag.split("}")[1]
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attributes.setdefault(tag, []).append(attribute.text)
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# Ensure a user was found.
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if user is None:
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raise CasError("no_user", "CAS response does not contain user")
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return CasResponse(user, attributes)
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async def handle_redirect_request(
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self,
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request: SynapseRequest,
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client_redirect_url: Optional[bytes],
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ui_auth_session_id: Optional[str] = None,
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) -> str:
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"""Generates a URL for the CAS server where the client should be redirected.
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Args:
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request: the incoming HTTP request
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client_redirect_url: the URL that we should redirect the
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client to after login (or None for UI Auth).
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ui_auth_session_id: The session ID of the ongoing UI Auth (or
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None if this is a login).
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Returns:
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URL to redirect to
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"""
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if ui_auth_session_id:
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service_args = {"session": ui_auth_session_id}
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else:
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assert client_redirect_url
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service_args = {"redirectUrl": client_redirect_url.decode("utf8")}
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args = urllib.parse.urlencode(
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{"service": self._build_service_param(service_args)}
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)
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return "%s/login?%s" % (self._cas_server_url, args)
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async def handle_ticket(
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self,
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request: SynapseRequest,
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ticket: str,
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client_redirect_url: Optional[str],
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session: Optional[str],
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) -> None:
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"""
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Called once the user has successfully authenticated with the SSO.
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Validates a CAS ticket sent by the client and completes the auth process.
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If the user interactive authentication session is provided, marks the
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UI Auth session as complete, then returns an HTML page notifying the
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user they are done.
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Otherwise, this registers the user if necessary, and then returns a
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redirect (with a login token) to the client.
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Args:
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request: the incoming request from the browser. We'll
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respond to it with a redirect or an HTML page.
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ticket: The CAS ticket provided by the client.
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client_redirect_url: the redirectUrl parameter from the `/cas/ticket` HTTP request, if given.
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This should be the same as the redirectUrl from the original `/login/sso/redirect` request.
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session: The session parameter from the `/cas/ticket` HTTP request, if given.
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This should be the UI Auth session id.
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"""
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args = {}
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if client_redirect_url:
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args["redirectUrl"] = client_redirect_url
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if session:
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args["session"] = session
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try:
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cas_response = await self._validate_ticket(ticket, args)
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except CasError as e:
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logger.exception("Could not validate ticket")
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self._sso_handler.render_error(request, e.error, e.error_description, 401)
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return
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await self._handle_cas_response(
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request, cas_response, client_redirect_url, session
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)
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async def _handle_cas_response(
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self,
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request: SynapseRequest,
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cas_response: CasResponse,
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client_redirect_url: Optional[str],
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session: Optional[str],
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) -> None:
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"""Handle a CAS response to a ticket request.
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Assumes that the response has been validated. Maps the user onto an MXID,
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registering them if necessary, and returns a response to the browser.
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Args:
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request: the incoming request from the browser. We'll respond to it with an
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HTML page or a redirect
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cas_response: The parsed CAS response.
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client_redirect_url: the redirectUrl parameter from the `/cas/ticket` HTTP request, if given.
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This should be the same as the redirectUrl from the original `/login/sso/redirect` request.
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session: The session parameter from the `/cas/ticket` HTTP request, if given.
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This should be the UI Auth session id.
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"""
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# first check if we're doing a UIA
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if session:
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return await self._sso_handler.complete_sso_ui_auth_request(
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self.idp_id,
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cas_response.username,
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session,
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request,
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)
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# otherwise, we're handling a login request.
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# Ensure that the attributes of the logged in user meet the required
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# attributes.
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if not self._sso_handler.check_required_attributes(
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request, cas_response.attributes, self._cas_required_attributes
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):
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return
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# Call the mapper to register/login the user
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# If this not a UI auth request than there must be a redirect URL.
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assert client_redirect_url is not None
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try:
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await self._complete_cas_login(cas_response, request, client_redirect_url)
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except MappingException as e:
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logger.exception("Could not map user")
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self._sso_handler.render_error(request, "mapping_error", str(e))
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async def _complete_cas_login(
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self,
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cas_response: CasResponse,
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request: SynapseRequest,
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client_redirect_url: str,
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) -> None:
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"""
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Given a CAS response, complete the login flow
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Retrieves the remote user ID, registers the user if necessary, and serves
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a redirect back to the client with a login-token.
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Args:
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cas_response: The parsed CAS response.
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request: The request to respond to
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client_redirect_url: The redirect URL passed in by the client.
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Raises:
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MappingException if there was a problem mapping the response to a user.
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RedirectException: some mapping providers may raise this if they need
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to redirect to an interstitial page.
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"""
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# Note that CAS does not support a mapping provider, so the logic is hard-coded.
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localpart = map_username_to_mxid_localpart(cas_response.username)
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async def cas_response_to_user_attributes(failures: int) -> UserAttributes:
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"""
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Map from CAS attributes to user attributes.
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"""
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# Due to the grandfathering logic matching any previously registered
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# mxids it isn't expected for there to be any failures.
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if failures:
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raise RuntimeError("CAS is not expected to de-duplicate Matrix IDs")
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# Arbitrarily use the first attribute found.
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display_name = cas_response.attributes.get(
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self._cas_displayname_attribute, [None]
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)[0]
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return UserAttributes(localpart=localpart, display_name=display_name)
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async def grandfather_existing_users() -> Optional[str]:
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# Since CAS did not always use the user_external_ids table, always
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# to attempt to map to existing users.
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user_id = UserID(localpart, self._hostname).to_string()
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logger.debug(
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"Looking for existing account based on mapped %s",
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user_id,
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)
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users = await self._store.get_users_by_id_case_insensitive(user_id)
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if users:
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registered_user_id = list(users.keys())[0]
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logger.info("Grandfathering mapping to %s", registered_user_id)
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return registered_user_id
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return None
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await self._sso_handler.complete_sso_login_request(
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self.idp_id,
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cas_response.username,
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request,
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client_redirect_url,
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cas_response_to_user_attributes,
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grandfather_existing_users,
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)
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