MatrixSynapse/synapse/handlers/cas_handler.py

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# -*- 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 urllib
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from typing import Dict, Optional, Tuple
from xml.etree import ElementTree as ET
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()
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def _build_service_param(self, args: Dict[str, str]) -> str:
"""
Generates a value to use as the "service" parameter when redirecting or
querying the CAS service.
Args:
args: Additional arguments to include in the final redirect URL.
Returns:
The URL to use as a "service" parameter.
"""
return "%s%s?%s" % (
self._cas_service_url,
"/_matrix/client/r0/login/cas/ticket",
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urllib.parse.urlencode(args),
)
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async def _validate_ticket(
self, ticket: str, service_args: Dict[str, str]
) -> Tuple[str, Optional[str]]:
"""
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Validate a CAS ticket with the server, parse the response, and return the user and display name.
Args:
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ticket: The CAS ticket from the client.
service_args: Additional arguments to include in the service URL.
Should be the same as those passed to `get_redirect_url`.
"""
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uri = self._cas_server_url + "/proxyValidate"
args = {
"ticket": ticket,
"service": self._build_service_param(service_args),
}
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
user, attributes = self._parse_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)
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return user, displayname
def _parse_cas_response(
self, cas_response_body: bytes
) -> 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
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def get_redirect_url(self, service_args: Dict[str, str]) -> str:
"""
Generates a URL for the CAS server where the client should be redirected.
Args:
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service_args: Additional arguments to include in the final redirect URL.
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Returns:
The URL to redirect the client to.
"""
args = urllib.parse.urlencode(
{"service": self._build_service_param(service_args)}
)
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return "%s/login?%s" % (self._cas_server_url, args)
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async def handle_ticket(
self,
request: SynapseRequest,
ticket: str,
client_redirect_url: Optional[str],
session: Optional[str],
) -> None:
"""
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Called once the user has successfully authenticated with the SSO.
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
UI Auth session as complete, then returns an HTML page notifying the
user they are done.
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Otherwise, this registers the user if necessary, and then returns a
redirect (with a login token) to the client.
Args:
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request: the incoming request from the browser. We'll
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.
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.
This should be the UI Auth session id.
"""
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args = {}
if client_redirect_url:
args["redirectUrl"] = client_redirect_url
if session:
args["session"] = session
username, user_display_name = await self._validate_ticket(ticket, args)
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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)
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if session:
await self._auth_handler.complete_sso_ui_auth(
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registered_user_id, session, request,
)
else:
if not registered_user_id:
registered_user_id = await self._registration_handler.register_user(
localpart=localpart, default_display_name=user_display_name
)
await self._auth_handler.complete_sso_login(
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registered_user_id, request, client_redirect_url
)