summary refs log tree commit diff
path: root/synapse/api/auth/oauth_delegated.py
blob: 5565ef0a1a73c26848a5c0bfb41aeac1f1f67586 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
# 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, 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 OAuthDelegatedAuth(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.auth
        assert self._config.oauth_delegation_enabled, "OAuth delegation is not enabled"
        assert self._config.oauth_delegation_issuer, "No issuer provided"
        assert self._config.oauth_delegation_client_id, "No client_id provided"
        assert self._config.oauth_delegation_client_secret, "No client_secret provided"
        assert (
            self._config.oauth_delegation_client_auth_method
            in OAuthDelegatedAuth.AUTH_METHODS
        ), "Invalid client_auth_method"

        self._http_client = hs.get_proxied_http_client()
        self._hostname = hs.hostname

        self._issuer_metadata = RetryOnExceptionCachedCall(self._load_metadata)
        secret = self._config.oauth_delegation_client_secret
        self._client_auth = ClientAuth(
            self._config.oauth_delegation_client_id,
            secret,
            OAuthDelegatedAuth.AUTH_METHODS[
                self._config.oauth_delegation_client_auth_method
            ],
        )

    async def _load_metadata(self) -> OpenIDProviderMetadata:
        if self._config.oauth_delegation_issuer_metadata is not None:
            return OpenIDProviderMetadata(
                **self._config.oauth_delegation_issuer_metadata
            )
        url = get_well_known_url(self._config.oauth_delegation_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)
        return await self.get_user_by_access_token(access_token, allow_expired)

    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 scopes
        #   - verify the audience
        if not introspection_result.get("active"):
            raise AuthError(
                403,
                "Invalid access token",
            )

        # Match via the sub claim
        sub: Optional[str] = introspection_result.get("sub")
        if sub is None:
            raise AuthError(500, "Invalid sub claim in the introspection result")

        user_id_str = await self.store.get_user_by_external_id(
            OAuthDelegatedAuth.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
                await self.store.register_user(user_id=user_id.to_string())

            # And record the sub as external_id
            await self.store.record_user_external_id(
                OAuthDelegatedAuth.EXTERNAL_ID_PROVIDER, sub, user_id.to_string()
            )
        else:
            user_id = UserID.from_string(user_id_str)

        # Let's look at the scope
        scope: List[str] = scope_to_list(introspection_result.get("scope", ""))
        device_id = None
        # Find device_id in scope
        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,
        )