google/oauth2/challenges.py

# 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

from google.auth import _helpers
from google.auth import exceptions


REAUTH_ORIGIN = "https://accounts.google.com"
SAML_CHALLENGE_MESSAGE = (
    "Please run `gcloud auth login` to complete reauthentication with SAML."
)


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)


class ReauthChallenge(object, metaclass=abc.ABCMeta):
    """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


class SamlChallenge(ReauthChallenge):
    """Challenge that asks the users to browse to their ID Providers.

    Currently SAML challenge is not supported. When obtaining the challenge
    input, exception will be raised to instruct the users to run
    `gcloud auth login` for reauthentication.
    """

    @property
    def name(self):
        return "SAML"

    @property
    def is_locally_eligible(self):
        return True

    def obtain_challenge_input(self, metadata):
        # Magic Arch has not fully supported returning a proper dedirect URL
        # for programmatic SAML users today. So we error our here and request
        # users to use gcloud to complete a login.
        raise exceptions.ReauthSamlChallengeFailError(SAML_CHALLENGE_MESSAGE)


AVAILABLE_CHALLENGES = {
    challenge.name: challenge
    for challenge in [SecurityKeyChallenge(), PasswordChallenge(), SamlChallenge()]
}