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# Copyright 2020 Quentin Gliech
# Copyright 2021 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.
"""Utilities for manipulating macaroons"""
from typing import Callable, Optional
import pymacaroons
from pymacaroons.exceptions import MacaroonVerificationFailedException
def get_value_from_macaroon(macaroon: pymacaroons.Macaroon, key: str) -> str:
"""Extracts a caveat value from a macaroon token.
Checks that there is exactly one caveat of the form "key = <val>" in the macaroon,
and returns the extracted value.
Args:
macaroon: the token
key: the key of the caveat to extract
Returns:
The extracted value
Raises:
MacaroonVerificationFailedException: if there are conflicting values for the
caveat in the macaroon, or if the caveat was not found in the macaroon.
"""
prefix = key + " = "
result: Optional[str] = None
for caveat in macaroon.caveats:
if not caveat.caveat_id.startswith(prefix):
continue
val = caveat.caveat_id[len(prefix) :]
if result is None:
# first time we found this caveat: record the value
result = val
elif val != result:
# on subsequent occurrences, raise if the value is different.
raise MacaroonVerificationFailedException(
"Conflicting values for caveat " + key
)
if result is not None:
return result
# If the caveat is not there, we raise a MacaroonVerificationFailedException.
# Note that it is insecure to generate a macaroon without all the caveats you
# might need (because there is nothing stopping people from adding extra caveats),
# so if the caveat isn't there, something odd must be going on.
raise MacaroonVerificationFailedException("No %s caveat in macaroon" % (key,))
def satisfy_expiry(v: pymacaroons.Verifier, get_time_ms: Callable[[], int]) -> None:
"""Make a macaroon verifier which accepts 'time' caveats
Builds a caveat verifier which will accept unexpired 'time' caveats, and adds it to
the given macaroon verifier.
Args:
v: the macaroon verifier
get_time_ms: a callable which will return the timestamp after which the caveat
should be considered expired. Normally the current time.
"""
def verify_expiry_caveat(caveat: str) -> bool:
time_msec = get_time_ms()
prefix = "time < "
if not caveat.startswith(prefix):
return False
expiry = int(caveat[len(prefix) :])
return time_msec < expiry
v.satisfy_general(verify_expiry_caveat)
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