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630d0aeaf6
PKCE can protect against certain attacks and is enabled by default. Support can be controlled manually by setting the pkce_method of each oidc_providers entry to 'auto' (default), 'always', or 'never'. This is required by Twitter OAuth 2.0 support.
319 lines
12 KiB
Python
319 lines
12 KiB
Python
# Copyright 2020 Quentin Gliech
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# Copyright 2021 The Matrix.org Foundation C.I.C.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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"""Utilities for manipulating macaroons"""
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from typing import Callable, Optional
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import attr
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import pymacaroons
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from pymacaroons.exceptions import MacaroonVerificationFailedException
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from typing_extensions import Literal
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from synapse.util import Clock, stringutils
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MacaroonType = Literal["access", "delete_pusher", "session"]
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def get_value_from_macaroon(macaroon: pymacaroons.Macaroon, key: str) -> str:
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"""Extracts a caveat value from a macaroon token.
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Checks that there is exactly one caveat of the form "key = <val>" in the macaroon,
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and returns the extracted value.
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Args:
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macaroon: the token
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key: the key of the caveat to extract
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Returns:
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The extracted value
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Raises:
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MacaroonVerificationFailedException: if there are conflicting values for the
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caveat in the macaroon, or if the caveat was not found in the macaroon.
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"""
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prefix = key + " = "
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result: Optional[str] = None
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for caveat in macaroon.caveats:
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if not caveat.caveat_id.startswith(prefix):
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continue
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val = caveat.caveat_id[len(prefix) :]
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if result is None:
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# first time we found this caveat: record the value
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result = val
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elif val != result:
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# on subsequent occurrences, raise if the value is different.
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raise MacaroonVerificationFailedException(
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"Conflicting values for caveat " + key
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)
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if result is not None:
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return result
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# If the caveat is not there, we raise a MacaroonVerificationFailedException.
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# Note that it is insecure to generate a macaroon without all the caveats you
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# might need (because there is nothing stopping people from adding extra caveats),
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# so if the caveat isn't there, something odd must be going on.
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raise MacaroonVerificationFailedException("No %s caveat in macaroon" % (key,))
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def satisfy_expiry(v: pymacaroons.Verifier, get_time_ms: Callable[[], int]) -> None:
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"""Make a macaroon verifier which accepts 'time' caveats
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Builds a caveat verifier which will accept unexpired 'time' caveats, and adds it to
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the given macaroon verifier.
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Args:
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v: the macaroon verifier
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get_time_ms: a callable which will return the timestamp after which the caveat
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should be considered expired. Normally the current time.
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"""
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def verify_expiry_caveat(caveat: str) -> bool:
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time_msec = get_time_ms()
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prefix = "time < "
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if not caveat.startswith(prefix):
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return False
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expiry = int(caveat[len(prefix) :])
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return time_msec < expiry
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v.satisfy_general(verify_expiry_caveat)
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@attr.s(frozen=True, slots=True, auto_attribs=True)
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class OidcSessionData:
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"""The attributes which are stored in a OIDC session cookie"""
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idp_id: str
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"""The Identity Provider being used"""
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nonce: str
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"""The `nonce` parameter passed to the OIDC provider."""
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client_redirect_url: str
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"""The URL the client gave when it initiated the flow. ("" if this is a UI Auth)"""
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ui_auth_session_id: str
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"""The session ID of the ongoing UI Auth ("" if this is a login)"""
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code_verifier: str
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"""The random string used in the RFC7636 code challenge ("" if PKCE is not being used)."""
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class MacaroonGenerator:
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def __init__(self, clock: Clock, location: str, secret_key: bytes):
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self._clock = clock
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self._location = location
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self._secret_key = secret_key
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def generate_guest_access_token(self, user_id: str) -> str:
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"""Generate a guest access token for the given user ID
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Args:
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user_id: The user ID for which the guest token should be generated.
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Returns:
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A signed access token for that guest user.
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"""
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nonce = stringutils.random_string_with_symbols(16)
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macaroon = self._generate_base_macaroon("access")
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macaroon.add_first_party_caveat(f"user_id = {user_id}")
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macaroon.add_first_party_caveat(f"nonce = {nonce}")
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macaroon.add_first_party_caveat("guest = true")
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return macaroon.serialize()
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def generate_delete_pusher_token(
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self, user_id: str, app_id: str, pushkey: str
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) -> str:
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"""Generate a signed token used for unsubscribing from email notifications
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Args:
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user_id: The user for which this token will be valid.
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app_id: The app_id for this pusher.
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pushkey: The unique identifier of this pusher.
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Returns:
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A signed token which can be used in unsubscribe links.
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"""
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macaroon = self._generate_base_macaroon("delete_pusher")
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macaroon.add_first_party_caveat(f"user_id = {user_id}")
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macaroon.add_first_party_caveat(f"app_id = {app_id}")
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macaroon.add_first_party_caveat(f"pushkey = {pushkey}")
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return macaroon.serialize()
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def generate_oidc_session_token(
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self,
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state: str,
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session_data: OidcSessionData,
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duration_in_ms: int = (60 * 60 * 1000),
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) -> str:
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"""Generates a signed token storing data about an OIDC session.
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When Synapse initiates an authorization flow, it creates a random state
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and a random nonce. Those parameters are given to the provider and
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should be verified when the client comes back from the provider.
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It is also used to store the client_redirect_url, which is used to
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complete the SSO login flow.
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Args:
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state: The ``state`` parameter passed to the OIDC provider.
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session_data: data to include in the session token.
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duration_in_ms: An optional duration for the token in milliseconds.
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Defaults to an hour.
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Returns:
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A signed macaroon token with the session information.
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"""
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now = self._clock.time_msec()
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expiry = now + duration_in_ms
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macaroon = self._generate_base_macaroon("session")
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macaroon.add_first_party_caveat(f"state = {state}")
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macaroon.add_first_party_caveat(f"idp_id = {session_data.idp_id}")
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macaroon.add_first_party_caveat(f"nonce = {session_data.nonce}")
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macaroon.add_first_party_caveat(
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f"client_redirect_url = {session_data.client_redirect_url}"
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)
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macaroon.add_first_party_caveat(
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f"ui_auth_session_id = {session_data.ui_auth_session_id}"
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)
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macaroon.add_first_party_caveat(f"code_verifier = {session_data.code_verifier}")
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macaroon.add_first_party_caveat(f"time < {expiry}")
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return macaroon.serialize()
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def verify_guest_token(self, token: str) -> str:
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"""Verify a guest access token macaroon
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Checks that the given token is a valid, unexpired guest access token
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minted by this server.
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Args:
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token: The access token to verify.
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Returns:
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The ``user_id`` that this token is valid for.
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Raises:
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MacaroonVerificationFailedException if the verification failed
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"""
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macaroon = pymacaroons.Macaroon.deserialize(token)
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user_id = get_value_from_macaroon(macaroon, "user_id")
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# At some point, Synapse would generate macaroons without the "guest"
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# caveat for regular users. Because of how macaroon verification works,
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# to avoid validating those as guest tokens, we explicitely verify if
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# the macaroon includes the "guest = true" caveat.
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is_guest = any(
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(caveat.caveat_id == "guest = true" for caveat in macaroon.caveats)
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)
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if not is_guest:
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raise MacaroonVerificationFailedException("Macaroon is not a guest token")
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v = self._base_verifier("access")
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v.satisfy_exact("guest = true")
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v.satisfy_general(lambda c: c.startswith("user_id = "))
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v.satisfy_general(lambda c: c.startswith("nonce = "))
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satisfy_expiry(v, self._clock.time_msec)
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v.verify(macaroon, self._secret_key)
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return user_id
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def verify_delete_pusher_token(self, token: str, app_id: str, pushkey: str) -> str:
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"""Verify a token from an email unsubscribe link
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Args:
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token: The token to verify.
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app_id: The app_id of the pusher to delete.
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pushkey: The unique identifier of the pusher to delete.
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Return:
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The ``user_id`` for which this token is valid.
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Raises:
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MacaroonVerificationFailedException if the verification failed
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"""
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macaroon = pymacaroons.Macaroon.deserialize(token)
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user_id = get_value_from_macaroon(macaroon, "user_id")
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v = self._base_verifier("delete_pusher")
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v.satisfy_exact(f"app_id = {app_id}")
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v.satisfy_exact(f"pushkey = {pushkey}")
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v.satisfy_general(lambda c: c.startswith("user_id = "))
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v.verify(macaroon, self._secret_key)
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return user_id
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def verify_oidc_session_token(self, session: bytes, state: str) -> OidcSessionData:
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"""Verifies and extract an OIDC session token.
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This verifies that a given session token was issued by this homeserver
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and extract the nonce and client_redirect_url caveats.
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Args:
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session: The session token to verify
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state: The state the OIDC provider gave back
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Returns:
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The data extracted from the session cookie
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Raises:
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KeyError if an expected caveat is missing from the macaroon.
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"""
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macaroon = pymacaroons.Macaroon.deserialize(session)
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v = self._base_verifier("session")
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v.satisfy_exact(f"state = {state}")
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v.satisfy_general(lambda c: c.startswith("nonce = "))
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v.satisfy_general(lambda c: c.startswith("idp_id = "))
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v.satisfy_general(lambda c: c.startswith("client_redirect_url = "))
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v.satisfy_general(lambda c: c.startswith("ui_auth_session_id = "))
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v.satisfy_general(lambda c: c.startswith("code_verifier = "))
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satisfy_expiry(v, self._clock.time_msec)
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v.verify(macaroon, self._secret_key)
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# Extract the session data from the token.
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nonce = get_value_from_macaroon(macaroon, "nonce")
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idp_id = get_value_from_macaroon(macaroon, "idp_id")
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client_redirect_url = get_value_from_macaroon(macaroon, "client_redirect_url")
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ui_auth_session_id = get_value_from_macaroon(macaroon, "ui_auth_session_id")
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code_verifier = get_value_from_macaroon(macaroon, "code_verifier")
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return OidcSessionData(
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nonce=nonce,
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idp_id=idp_id,
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client_redirect_url=client_redirect_url,
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ui_auth_session_id=ui_auth_session_id,
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code_verifier=code_verifier,
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)
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def _generate_base_macaroon(self, type: MacaroonType) -> pymacaroons.Macaroon:
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macaroon = pymacaroons.Macaroon(
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location=self._location,
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identifier="key",
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key=self._secret_key,
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)
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macaroon.add_first_party_caveat("gen = 1")
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macaroon.add_first_party_caveat(f"type = {type}")
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return macaroon
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def _base_verifier(self, type: MacaroonType) -> pymacaroons.Verifier:
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v = pymacaroons.Verifier()
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v.satisfy_exact("gen = 1")
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v.satisfy_exact(f"type = {type}")
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return v
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