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# Copyright 2016 Google LLC
#
# 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.
"""Base classes for cryptographic signers and verifiers."""
import abc
import io
import json
import six
_JSON_FILE_PRIVATE_KEY = "private_key"
_JSON_FILE_PRIVATE_KEY_ID = "private_key_id"
@six.add_metaclass(abc.ABCMeta)
class Verifier(object):
"""Abstract base class for crytographic signature verifiers."""
@abc.abstractmethod
def verify(self, message, signature):
"""Verifies a message against a cryptographic signature.
Args:
message (Union[str, bytes]): The message to verify.
signature (Union[str, bytes]): The cryptography signature to check.
Returns:
bool: True if message was signed by the private key associated
with the public key that this object was constructed with.
"""
# pylint: disable=missing-raises-doc,redundant-returns-doc
# (pylint doesn't recognize that this is abstract)
raise NotImplementedError("Verify must be implemented")
@six.add_metaclass(abc.ABCMeta)
class Signer(object):
"""Abstract base class for cryptographic signers."""
@abc.abstractproperty
def key_id(self):
"""Optional[str]: The key ID used to identify this private key."""
raise NotImplementedError("Key id must be implemented")
@abc.abstractmethod
def sign(self, message):
"""Signs a message.
Args:
message (Union[str, bytes]): The message to be signed.
Returns:
bytes: The signature of the message.
"""
# pylint: disable=missing-raises-doc,redundant-returns-doc
# (pylint doesn't recognize that this is abstract)
raise NotImplementedError("Sign must be implemented")
@six.add_metaclass(abc.ABCMeta)
class FromServiceAccountMixin(object):
"""Mix-in to enable factory constructors for a Signer."""
@abc.abstractmethod
def from_string(cls, key, key_id=None):
"""Construct an Signer instance from a private key string.
Args:
key (str): Private key as a string.
key_id (str): An optional key id used to identify the private key.
Returns:
google.auth.crypt.Signer: The constructed signer.
Raises:
ValueError: If the key cannot be parsed.
"""
raise NotImplementedError("from_string must be implemented")
@classmethod
def from_service_account_info(cls, info):
"""Creates a Signer instance instance from a dictionary containing
service account info in Google format.
Args:
info (Mapping[str, str]): The service account info in Google
format.
Returns:
google.auth.crypt.Signer: The constructed signer.
Raises:
ValueError: If the info is not in the expected format.
"""
if _JSON_FILE_PRIVATE_KEY not in info:
raise ValueError(
"The private_key field was not found in the service account " "info."
)
return cls.from_string(
info[_JSON_FILE_PRIVATE_KEY], info.get(_JSON_FILE_PRIVATE_KEY_ID)
)
@classmethod
def from_service_account_file(cls, filename):
"""Creates a Signer instance from a service account .json file
in Google format.
Args:
filename (str): The path to the service account .json file.
Returns:
google.auth.crypt.Signer: The constructed signer.
"""
with io.open(filename, "r", encoding="utf-8") as json_file:
data = json.load(json_file)
return cls.from_service_account_info(data)
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