summary refs log tree commit diff
path: root/synapse/handlers/saml_handler.py
blob: 0082f85c2666ada1a5e4873d4f4978cf171fedf9 (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
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
# -*- coding: utf-8 -*-
# Copyright 2019 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 re
from typing import Tuple

import attr
import saml2
import saml2.response
from saml2.client import Saml2Client

from synapse.api.errors import SynapseError
from synapse.config import ConfigError
from synapse.http.servlet import parse_string
from synapse.rest.client.v1.login import SSOAuthHandler
from synapse.types import (
    UserID,
    map_username_to_mxid_localpart,
    mxid_localpart_allowed_characters,
)
from synapse.util.async_helpers import Linearizer

logger = logging.getLogger(__name__)


@attr.s
class Saml2SessionData:
    """Data we track about SAML2 sessions"""

    # time the session was created, in milliseconds
    creation_time = attr.ib()


class SamlHandler:
    def __init__(self, hs):
        self._saml_client = Saml2Client(hs.config.saml2_sp_config)
        self._sso_auth_handler = SSOAuthHandler(hs)
        self._registration_handler = hs.get_registration_handler()

        self._clock = hs.get_clock()
        self._datastore = hs.get_datastore()
        self._hostname = hs.hostname
        self._saml2_session_lifetime = hs.config.saml2_session_lifetime
        self._grandfathered_mxid_source_attribute = (
            hs.config.saml2_grandfathered_mxid_source_attribute
        )

        # plugin to do custom mapping from saml response to mxid
        self._user_mapping_provider = hs.config.saml2_user_mapping_provider_class(
            hs.config.saml2_user_mapping_provider_config
        )

        # identifier for the external_ids table
        self._auth_provider_id = "saml"

        # a map from saml session id to Saml2SessionData object
        self._outstanding_requests_dict = {}

        # a lock on the mappings
        self._mapping_lock = Linearizer(name="saml_mapping", clock=self._clock)

    def handle_redirect_request(self, client_redirect_url):
        """Handle an incoming request to /login/sso/redirect

        Args:
            client_redirect_url (bytes): the URL that we should redirect the
                client to when everything is done

        Returns:
            bytes: URL to redirect to
        """
        reqid, info = self._saml_client.prepare_for_authenticate(
            relay_state=client_redirect_url
        )

        now = self._clock.time_msec()
        self._outstanding_requests_dict[reqid] = Saml2SessionData(creation_time=now)

        for key, value in info["headers"]:
            if key == "Location":
                return value

        # this shouldn't happen!
        raise Exception("prepare_for_authenticate didn't return a Location header")

    async def handle_saml_response(self, request):
        """Handle an incoming request to /_matrix/saml2/authn_response

        Args:
            request (SynapseRequest): the incoming request from the browser. We'll
                respond to it with a redirect.

        Returns:
            Deferred[none]: Completes once we have handled the request.
        """
        resp_bytes = parse_string(request, "SAMLResponse", required=True)
        relay_state = parse_string(request, "RelayState", required=True)

        # expire outstanding sessions before parse_authn_request_response checks
        # the dict.
        self.expire_sessions()

        user_id = await self._map_saml_response_to_user(resp_bytes)
        self._sso_auth_handler.complete_sso_login(user_id, request, relay_state)

    async def _map_saml_response_to_user(self, resp_bytes):
        try:
            saml2_auth = self._saml_client.parse_authn_request_response(
                resp_bytes,
                saml2.BINDING_HTTP_POST,
                outstanding=self._outstanding_requests_dict,
            )
        except Exception as e:
            logger.warning("Exception parsing SAML2 response: %s", e)
            raise SynapseError(400, "Unable to parse SAML2 response: %s" % (e,))

        if saml2_auth.not_signed:
            logger.warning("SAML2 response was not signed")
            raise SynapseError(400, "SAML2 response was not signed")

        logger.info("SAML2 response: %s", saml2_auth.origxml)
        logger.info("SAML2 mapped attributes: %s", saml2_auth.ava)

        try:
            remote_user_id = saml2_auth.ava["uid"][0]
        except KeyError:
            logger.warning("SAML2 response lacks a 'uid' attestation")
            raise SynapseError(400, "'uid' not in SAML2 response")

        self._outstanding_requests_dict.pop(saml2_auth.in_response_to, None)

        with (await self._mapping_lock.queue(self._auth_provider_id)):
            # first of all, check if we already have a mapping for this user
            logger.info(
                "Looking for existing mapping for user %s:%s",
                self._auth_provider_id,
                remote_user_id,
            )
            registered_user_id = await self._datastore.get_user_by_external_id(
                self._auth_provider_id, remote_user_id
            )
            if registered_user_id is not None:
                logger.info("Found existing mapping %s", registered_user_id)
                return registered_user_id

            # backwards-compatibility hack: see if there is an existing user with a
            # suitable mapping from the uid
            if (
                self._grandfathered_mxid_source_attribute
                and self._grandfathered_mxid_source_attribute in saml2_auth.ava
            ):
                attrval = saml2_auth.ava[self._grandfathered_mxid_source_attribute][0]
                user_id = UserID(
                    map_username_to_mxid_localpart(attrval), self._hostname
                ).to_string()
                logger.info(
                    "Looking for existing account based on mapped %s %s",
                    self._grandfathered_mxid_source_attribute,
                    user_id,
                )

                users = await self._datastore.get_users_by_id_case_insensitive(user_id)
                if users:
                    registered_user_id = list(users.keys())[0]
                    logger.info("Grandfathering mapping to %s", registered_user_id)
                    await self._datastore.record_user_external_id(
                        self._auth_provider_id, remote_user_id, registered_user_id
                    )
                    return registered_user_id

            # Map saml response to user attributes using the configured mapping provider
            for i in range(1000):
                attribute_dict = self._user_mapping_provider.saml_response_to_user_attributes(
                    saml2_auth, i
                )

                logger.debug(
                    "Retrieved SAML attributes from user mapping provider: %s "
                    "(attempt %d)",
                    attribute_dict,
                    i,
                )

                localpart = attribute_dict.get("mxid_localpart")
                if not localpart:
                    logger.error(
                        "SAML mapping provider plugin did not return a "
                        "mxid_localpart object"
                    )
                    raise SynapseError(500, "Error parsing SAML2 response")

                displayname = attribute_dict.get("displayname")

                # Check if this mxid already exists
                if not await self._datastore.get_users_by_id_case_insensitive(
                    UserID(localpart, self._hostname).to_string()
                ):
                    # This mxid is free
                    break
            else:
                # Unable to generate a username in 1000 iterations
                # Break and return error to the user
                raise SynapseError(
                    500, "Unable to generate a Matrix ID from the SAML response"
                )

            registered_user_id = await self._registration_handler.register_user(
                localpart=localpart, default_display_name=displayname
            )

            await self._datastore.record_user_external_id(
                self._auth_provider_id, remote_user_id, registered_user_id
            )
            return registered_user_id

    def expire_sessions(self):
        expire_before = self._clock.time_msec() - self._saml2_session_lifetime
        to_expire = set()
        for reqid, data in self._outstanding_requests_dict.items():
            if data.creation_time < expire_before:
                to_expire.add(reqid)
        for reqid in to_expire:
            logger.debug("Expiring session id %s", reqid)
            del self._outstanding_requests_dict[reqid]


DOT_REPLACE_PATTERN = re.compile(
    ("[^%s]" % (re.escape("".join(mxid_localpart_allowed_characters)),))
)


def dot_replace_for_mxid(username: str) -> str:
    username = username.lower()
    username = DOT_REPLACE_PATTERN.sub(".", username)

    # regular mxids aren't allowed to start with an underscore either
    username = re.sub("^_", "", username)
    return username


MXID_MAPPER_MAP = {
    "hexencode": map_username_to_mxid_localpart,
    "dotreplace": dot_replace_for_mxid,
}


@attr.s
class SamlConfig(object):
    mxid_source_attribute = attr.ib()
    mxid_mapper = attr.ib()


class DefaultSamlMappingProvider(object):
    __version__ = "0.0.1"

    def __init__(self, parsed_config: SamlConfig):
        """The default SAML user mapping provider

        Args:
            parsed_config: Module configuration
        """
        self._mxid_source_attribute = parsed_config.mxid_source_attribute
        self._mxid_mapper = parsed_config.mxid_mapper

    def saml_response_to_user_attributes(
        self, saml_response: saml2.response.AuthnResponse, failures: int = 0,
    ) -> dict:
        """Maps some text from a SAML response to attributes of a new user

        Args:
            saml_response: A SAML auth response object

            failures: How many times a call to this function with this
                saml_response has resulted in a failure

        Returns:
            dict: A dict containing new user attributes. Possible keys:
                * mxid_localpart (str): Required. The localpart of the user's mxid
                * displayname (str): The displayname of the user
        """
        try:
            mxid_source = saml_response.ava[self._mxid_source_attribute][0]
        except KeyError:
            logger.warning(
                "SAML2 response lacks a '%s' attestation", self._mxid_source_attribute,
            )
            raise SynapseError(
                400, "%s not in SAML2 response" % (self._mxid_source_attribute,)
            )

        # Use the configured mapper for this mxid_source
        base_mxid_localpart = self._mxid_mapper(mxid_source)

        # Append suffix integer if last call to this function failed to produce
        # a usable mxid
        localpart = base_mxid_localpart + (str(failures) if failures else "")

        # Retrieve the display name from the saml response
        # If displayname is None, the mxid_localpart will be used instead
        displayname = saml_response.ava.get("displayName", [None])[0]

        return {
            "mxid_localpart": localpart,
            "displayname": displayname,
        }

    @staticmethod
    def parse_config(config: dict) -> SamlConfig:
        """Parse the dict provided by the homeserver's config
        Args:
            config: A dictionary containing configuration options for this provider
        Returns:
            SamlConfig: A custom config object for this module
        """
        # Parse config options and use defaults where necessary
        mxid_source_attribute = config.get("mxid_source_attribute", "uid")
        mapping_type = config.get("mxid_mapping", "hexencode")

        # Retrieve the associating mapping function
        try:
            mxid_mapper = MXID_MAPPER_MAP[mapping_type]
        except KeyError:
            raise ConfigError(
                "saml2_config.user_mapping_provider.config: '%s' is not a valid "
                "mxid_mapping value" % (mapping_type,)
            )

        return SamlConfig(mxid_source_attribute, mxid_mapper)

    @staticmethod
    def get_saml_attributes(config: SamlConfig) -> Tuple[set, set]:
        """Returns the required attributes of a SAML

        Args:
            config: A SamlConfig object containing configuration params for this provider

        Returns:
            tuple[set,set]: The first set equates to the saml auth response
                attributes that are required for the module to function, whereas the
                second set consists of those attributes which can be used if
                available, but are not necessary
        """
        return {"uid", config.mxid_source_attribute}, {"displayName"}