diff options
Diffstat (limited to 'synapse/api/auth/msc3861_delegated.py')
| -rw-r--r-- | synapse/api/auth/msc3861_delegated.py | 280 |
1 files changed, 280 insertions, 0 deletions
diff --git a/synapse/api/auth/msc3861_delegated.py b/synapse/api/auth/msc3861_delegated.py new file mode 100644 index 0000000000..4ca3280bd3 --- /dev/null +++ b/synapse/api/auth/msc3861_delegated.py @@ -0,0 +1,280 @@ +# Copyright 2023 The Matrix.org Foundation. +# +# 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, Any, Dict, List, Optional +from urllib.parse import urlencode + +from authlib.oauth2 import ClientAuth +from authlib.oauth2.auth import encode_client_secret_basic, encode_client_secret_post +from authlib.oauth2.rfc7523 import ClientSecretJWT, PrivateKeyJWT, private_key_jwt_sign +from authlib.oauth2.rfc7662 import IntrospectionToken +from authlib.oidc.discovery import OpenIDProviderMetadata, get_well_known_url + +from twisted.web.client import readBody +from twisted.web.http_headers import Headers + +from synapse.api.auth.base import BaseAuth +from synapse.api.errors import ( + AuthError, + InvalidClientTokenError, + OAuthInsufficientScopeError, + StoreError, +) +from synapse.http.site import SynapseRequest +from synapse.logging.context import make_deferred_yieldable +from synapse.types import Requester, UserID, create_requester +from synapse.util import json_decoder +from synapse.util.caches.cached_call import RetryOnExceptionCachedCall + +if TYPE_CHECKING: + from synapse.server import HomeServer + +logger = logging.getLogger(__name__) + + +def scope_to_list(scope: str) -> List[str]: + """Convert a scope string to a list of scope tokens""" + return scope.strip().split(" ") + + +class PrivateKeyJWTWithKid(PrivateKeyJWT): + """An implementation of the private_key_jwt client auth method that includes a kid header. + + This is needed because some providers (Keycloak) require the kid header to figure + out which key to use to verify the signature. + """ + + def sign(self, auth: Any, token_endpoint: str) -> bytes: + return private_key_jwt_sign( + auth.client_secret, + client_id=auth.client_id, + token_endpoint=token_endpoint, + claims=self.claims, + header={"kid": auth.client_secret["kid"]}, + ) + + +class MSC3861DelegatedAuth(BaseAuth): + AUTH_METHODS = { + "client_secret_post": encode_client_secret_post, + "client_secret_basic": encode_client_secret_basic, + "client_secret_jwt": ClientSecretJWT(), + "private_key_jwt": PrivateKeyJWTWithKid(), + } + + EXTERNAL_ID_PROVIDER = "oauth-delegated" + + def __init__(self, hs: "HomeServer"): + super().__init__(hs) + + self._config = hs.config.experimental.msc3861 + auth_method = MSC3861DelegatedAuth.AUTH_METHODS.get( + self._config.client_auth_method.value, None + ) + # Those assertions are already checked when parsing the config + assert self._config.enabled, "OAuth delegation is not enabled" + assert self._config.issuer, "No issuer provided" + assert self._config.client_id, "No client_id provided" + assert auth_method is not None, "Invalid client_auth_method provided" + + self._http_client = hs.get_proxied_http_client() + self._hostname = hs.hostname + + self._issuer_metadata = RetryOnExceptionCachedCall(self._load_metadata) + + if isinstance(auth_method, PrivateKeyJWTWithKid): + # Use the JWK as the client secret when using the private_key_jwt method + assert self._config.jwk, "No JWK provided" + self._client_auth = ClientAuth( + self._config.client_id, self._config.jwk, auth_method + ) + else: + # Else use the client secret + assert self._config.client_secret, "No client_secret provided" + self._client_auth = ClientAuth( + self._config.client_id, self._config.client_secret, auth_method + ) + + async def _load_metadata(self) -> OpenIDProviderMetadata: + if self._config.issuer_metadata is not None: + return OpenIDProviderMetadata(**self._config.issuer_metadata) + url = get_well_known_url(self._config.issuer, external=True) + response = await self._http_client.get_json(url) + metadata = OpenIDProviderMetadata(**response) + # metadata.validate_introspection_endpoint() + return metadata + + async def _introspect_token(self, token: str) -> IntrospectionToken: + metadata = await self._issuer_metadata.get() + introspection_endpoint = metadata.get("introspection_endpoint") + raw_headers: Dict[str, str] = { + "Content-Type": "application/x-www-form-urlencoded", + "User-Agent": str(self._http_client.user_agent, "utf-8"), + "Accept": "application/json", + } + + args = {"token": token, "token_type_hint": "access_token"} + body = urlencode(args, True) + + # Fill the body/headers with credentials + uri, raw_headers, body = self._client_auth.prepare( + method="POST", uri=introspection_endpoint, headers=raw_headers, body=body + ) + headers = Headers({k: [v] for (k, v) in raw_headers.items()}) + + # Do the actual request + # We're not using the SimpleHttpClient util methods as we don't want to + # check the HTTP status code and we do the body encoding ourself. + response = await self._http_client.request( + method="POST", + uri=uri, + data=body.encode("utf-8"), + headers=headers, + ) + + resp_body = await make_deferred_yieldable(readBody(response)) + # TODO: Let's not worry about 5xx errors & co. for now and just try + # decoding that as JSON. We should also do some validation of the + # response + resp = json_decoder.decode(resp_body.decode("utf-8")) + return IntrospectionToken(**resp) + + async def is_server_admin(self, requester: Requester) -> bool: + return "urn:synapse:admin:*" in requester.scope + + async def get_user_by_req( + self, + request: SynapseRequest, + allow_guest: bool = False, + allow_expired: bool = False, + ) -> Requester: + access_token = self.get_access_token_from_request(request) + + # TODO: we probably want to assert the allow_guest inside this call so that we don't provision the user if they don't have enough permission: + requester = await self.get_user_by_access_token(access_token, allow_expired) + + if not allow_guest and requester.is_guest: + raise OAuthInsufficientScopeError( + ["urn:matrix:org.matrix.msc2967.client:api:*"] + ) + + return requester + + async def get_user_by_access_token( + self, + token: str, + allow_expired: bool = False, + ) -> Requester: + introspection_result = await self._introspect_token(token) + + logger.info(f"Introspection result: {introspection_result!r}") + + # TODO: introspection verification should be more extensive, especially: + # - verify the audience + if not introspection_result.get("active"): + raise InvalidClientTokenError("Token is not active") + + # Let's look at the scope + scope: List[str] = scope_to_list(introspection_result.get("scope", "")) + + # Determine type of user based on presence of particular scopes + has_admin_scope = "urn:synapse:admin:*" in scope + has_user_scope = "urn:matrix:org.matrix.msc2967.client:api:*" in scope + has_guest_scope = "urn:matrix:org.matrix.msc2967.client:api:guest" in scope + is_user = has_user_scope or has_admin_scope + is_guest = has_guest_scope and not is_user + + if not is_user and not is_guest: + raise InvalidClientTokenError("No scope in token granting user rights") + + # Match via the sub claim + sub: Optional[str] = introspection_result.get("sub") + if sub is None: + raise InvalidClientTokenError( + "Invalid sub claim in the introspection result" + ) + + user_id_str = await self.store.get_user_by_external_id( + MSC3861DelegatedAuth.EXTERNAL_ID_PROVIDER, sub + ) + if user_id_str is None: + # If we could not find a user via the external_id, it either does not exist, + # or the external_id was never recorded + + # TODO: claim mapping should be configurable + username: Optional[str] = introspection_result.get("username") + if username is None or not isinstance(username, str): + raise AuthError( + 500, + "Invalid username claim in the introspection result", + ) + user_id = UserID(username, self._hostname) + + # First try to find a user from the username claim + user_info = await self.store.get_userinfo_by_id(user_id=user_id.to_string()) + if user_info is None: + # If the user does not exist, we should create it on the fly + # TODO: we could use SCIM to provision users ahead of time and listen + # for SCIM SET events if those ever become standard: + # https://datatracker.ietf.org/doc/html/draft-hunt-scim-notify-00 + + # TODO: claim mapping should be configurable + # If present, use the name claim as the displayname + name: Optional[str] = introspection_result.get("name") + + await self.store.register_user( + user_id=user_id.to_string(), create_profile_with_displayname=name + ) + + # And record the sub as external_id + await self.store.record_user_external_id( + MSC3861DelegatedAuth.EXTERNAL_ID_PROVIDER, sub, user_id.to_string() + ) + else: + user_id = UserID.from_string(user_id_str) + + # Find device_id in scope + device_id = None + for tok in scope: + if tok.startswith("urn:matrix:org.matrix.msc2967.client:device:"): + parts = tok.split(":") + if len(parts) == 5: + device_id = parts[4] + + if device_id: + # Create the device on the fly if it does not exist + try: + await self.store.get_device( + user_id=user_id.to_string(), device_id=device_id + ) + except StoreError: + await self.store.store_device( + user_id=user_id.to_string(), + device_id=device_id, + initial_device_display_name="OIDC-native client", + ) + + # TODO: there is a few things missing in the requester here, which still need + # to be figured out, like: + # - impersonation, with the `authenticated_entity`, which is used for + # rate-limiting, MAU limits, etc. + # - shadow-banning, with the `shadow_banned` flag + # - a proper solution for appservices, which still needs to be figured out in + # the context of MSC3861 + return create_requester( + user_id=user_id, + device_id=device_id, + scope=scope, + is_guest=is_guest, + ) |