89 lines
3.1 KiB
Python
89 lines
3.1 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 pymacaroons
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from pymacaroons.exceptions import MacaroonVerificationFailedException
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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):
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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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