google/auth/_credentials_base.py

# Copyright 2024 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.


"""Interface for base credentials."""

import abc

from google.auth import _helpers


class _BaseCredentials(metaclass=abc.ABCMeta):
    """Base class for all credentials.

    All credentials have a :attr:`token` that is used for authentication and
    may also optionally set an :attr:`expiry` to indicate when the token will
    no longer be valid.

    Most credentials will be :attr:`invalid` until :meth:`refresh` is called.
    Credentials can do this automatically before the first HTTP request in
    :meth:`before_request`.

    Although the token and expiration will change as the credentials are
    :meth:`refreshed <refresh>` and used, credentials should be considered
    immutable. Various credentials will accept configuration such as private
    keys, scopes, and other options. These options are not changeable after
    construction. Some classes will provide mechanisms to copy the credentials
    with modifications such as :meth:`ScopedCredentials.with_scopes`.

    Attributes:
        token (Optional[str]): The bearer token that can be used in HTTP headers to make
            authenticated requests.
    """

    def __init__(self):
        self.token = None

    @abc.abstractmethod
    def refresh(self, request):
        """Refreshes the access token.

        Args:
            request (google.auth.transport.Request): The object used to make
                HTTP requests.

        Raises:
            google.auth.exceptions.RefreshError: If the credentials could
                not be refreshed.
        """
        # pylint: disable=missing-raises-doc
        # (pylint doesn't recognize that this is abstract)
        raise NotImplementedError("Refresh must be implemented")

    def _apply(self, headers, token=None):
        """Apply the token to the authentication header.

        Args:
            headers (Mapping): The HTTP request headers.
            token (Optional[str]): If specified, overrides the current access
                token.
        """
        headers["authorization"] = "Bearer {}".format(
            _helpers.from_bytes(token or self.token)
        )