1# Copyright 2024 Google LLC
2#
3# Licensed under the Apache License, Version 2.0 (the "License");
4# you may not use this file except in compliance with the License.
5# You may obtain a copy of the License at
6#
7# http://www.apache.org/licenses/LICENSE-2.0
8#
9# Unless required by applicable law or agreed to in writing, software
10# distributed under the License is distributed on an "AS IS" BASIS,
11# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12# See the License for the specific language governing permissions and
13# limitations under the License.
14
15
16"""Interface for base credentials."""
17
18import abc
19
20from google.auth import _helpers
21
22
23class _BaseCredentials(metaclass=abc.ABCMeta):
24 """Base class for all credentials.
25
26 All credentials have a :attr:`token` that is used for authentication and
27 may also optionally set an :attr:`expiry` to indicate when the token will
28 no longer be valid.
29
30 Most credentials will be :attr:`invalid` until :meth:`refresh` is called.
31 Credentials can do this automatically before the first HTTP request in
32 :meth:`before_request`.
33
34 Although the token and expiration will change as the credentials are
35 :meth:`refreshed <refresh>` and used, credentials should be considered
36 immutable. Various credentials will accept configuration such as private
37 keys, scopes, and other options. These options are not changeable after
38 construction. Some classes will provide mechanisms to copy the credentials
39 with modifications such as :meth:`ScopedCredentials.with_scopes`.
40
41 Attributes:
42 token (Optional[str]): The bearer token that can be used in HTTP headers to make
43 authenticated requests.
44 """
45
46 def __init__(self):
47 self.token = None
48
49 @abc.abstractmethod
50 def refresh(self, request):
51 """Refreshes the access token.
52
53 Args:
54 request (google.auth.transport.Request): The object used to make
55 HTTP requests.
56
57 Raises:
58 google.auth.exceptions.RefreshError: If the credentials could
59 not be refreshed.
60 """
61 # pylint: disable=missing-raises-doc
62 # (pylint doesn't recognize that this is abstract)
63 raise NotImplementedError("Refresh must be implemented")
64
65 def _apply(self, headers, token=None):
66 """Apply the token to the authentication header.
67
68 Args:
69 headers (Mapping): The HTTP request headers.
70 token (Optional[str]): If specified, overrides the current access
71 token.
72 """
73 headers["authorization"] = "Bearer {}".format(
74 _helpers.from_bytes(token or self.token)
75 )