Refactor the CAS code to move the logic to a handler

changelog.d/7136.misc

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+Refactored the CAS authentication logic to a separate class.

synapse/handlers/cas_handler.py

@@ -0,0 +1,204 @@
+# -*- 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)