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# Copyright 2021 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.
""" Challenges for reauthentication.
"""
import abc
import base64
import getpass
import sys
import six
from google.auth import _helpers
from google.auth import exceptions
REAUTH_ORIGIN = "https://accounts.google.com"
def get_user_password(text):
"""Get password from user.
Override this function with a different logic if you are using this library
outside a CLI.
Args:
text (str): message for the password prompt.
Returns:
str: password string.
"""
return getpass.getpass(text)
@six.add_metaclass(abc.ABCMeta)
class ReauthChallenge(object):
"""Base class for reauth challenges."""
@property
@abc.abstractmethod
def name(self): # pragma: NO COVER
"""Returns the name of the challenge."""
raise NotImplementedError("name property must be implemented")
@property
@abc.abstractmethod
def is_locally_eligible(self): # pragma: NO COVER
"""Returns true if a challenge is supported locally on this machine."""
raise NotImplementedError("is_locally_eligible property must be implemented")
@abc.abstractmethod
def obtain_challenge_input(self, metadata): # pragma: NO COVER
"""Performs logic required to obtain credentials and returns it.
Args:
metadata (Mapping): challenge metadata returned in the 'challenges' field in
the initial reauth request. Includes the 'challengeType' field
and other challenge-specific fields.
Returns:
response that will be send to the reauth service as the content of
the 'proposalResponse' field in the request body. Usually a dict
with the keys specific to the challenge. For example,
``{'credential': password}`` for password challenge.
"""
raise NotImplementedError("obtain_challenge_input method must be implemented")
class PasswordChallenge(ReauthChallenge):
"""Challenge that asks for user's password."""
@property
def name(self):
return "PASSWORD"
@property
def is_locally_eligible(self):
return True
@_helpers.copy_docstring(ReauthChallenge)
def obtain_challenge_input(self, unused_metadata):
passwd = get_user_password("Please enter your password:")
if not passwd:
passwd = " " # avoid the server crashing in case of no password :D
return {"credential": passwd}
class SecurityKeyChallenge(ReauthChallenge):
"""Challenge that asks for user's security key touch."""
@property
def name(self):
return "SECURITY_KEY"
@property
def is_locally_eligible(self):
return True
@_helpers.copy_docstring(ReauthChallenge)
def obtain_challenge_input(self, metadata):
try:
import pyu2f.convenience.authenticator
import pyu2f.errors
import pyu2f.model
except ImportError:
raise exceptions.ReauthFailError(
"pyu2f dependency is required to use Security key reauth feature. "
"It can be installed via `pip install pyu2f` or `pip install google-auth[reauth]`."
)
sk = metadata["securityKey"]
challenges = sk["challenges"]
app_id = sk["applicationId"]
challenge_data = []
for c in challenges:
kh = c["keyHandle"].encode("ascii")
key = pyu2f.model.RegisteredKey(bytearray(base64.urlsafe_b64decode(kh)))
challenge = c["challenge"].encode("ascii")
challenge = base64.urlsafe_b64decode(challenge)
challenge_data.append({"key": key, "challenge": challenge})
try:
api = pyu2f.convenience.authenticator.CreateCompositeAuthenticator(
REAUTH_ORIGIN
)
response = api.Authenticate(
app_id, challenge_data, print_callback=sys.stderr.write
)
return {"securityKey": response}
except pyu2f.errors.U2FError as e:
if e.code == pyu2f.errors.U2FError.DEVICE_INELIGIBLE:
sys.stderr.write("Ineligible security key.\n")
elif e.code == pyu2f.errors.U2FError.TIMEOUT:
sys.stderr.write("Timed out while waiting for security key touch.\n")
else:
raise e
except pyu2f.errors.NoDeviceFoundError:
sys.stderr.write("No security key found.\n")
return None
AVAILABLE_CHALLENGES = {
challenge.name: challenge
for challenge in [SecurityKeyChallenge(), PasswordChallenge()]
}
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