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# Copyright 2022 The Sigstore Authors
#
# 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.
"""
API for retrieving OIDC tokens.
"""
from __future__ import annotations
import base64
import binascii
import json
from typing import Callable
__version__ = "1.6.1"
class IdentityError(Exception):
"""
Raised on any OIDC token format or claim error.
"""
pass
class AmbientCredentialError(IdentityError):
"""
Raised when an ambient credential should be present, but
can't be retrieved (e.g. network failure).
"""
pass
class GitHubOidcPermissionCredentialError(AmbientCredentialError):
"""
Raised when the current GitHub Actions environment doesn't have permission
to retrieve an OIDC token.
"""
pass
def _validate_credential(credential: str, audience: str) -> None:
# Decode credential to verify it roughly looks like a token and contains
# the correct audience
try:
_, payload, _ = credential.split(".")
decoded_payload = base64.urlsafe_b64decode(payload + "==").decode("utf-8")
payload_json = json.loads(decoded_payload)
except (ValueError, binascii.Error, json.decoder.JSONDecodeError) as e:
raise AmbientCredentialError("Malformed token") from e
if not isinstance(payload_json, dict):
raise AmbientCredentialError("Malformed token payload (JWT is not a JSON object)")
if "aud" not in payload_json:
raise AmbientCredentialError("Malformed token payload (audience claim is missing)")
if payload_json["aud"] != audience:
raise AmbientCredentialError(
f"Token audience claim mismatch (expected {audience}, got {payload_json['aud']})"
)
def detect_credential(audience: str) -> str | None:
"""
Try each ambient credential detector, returning the first one to succeed
or `None` if all fail.
Raises `AmbientCredentialError` if any detector fails internally (i.e.
detects a credential, but cannot retrieve it).
"""
from ._internal.oidc.ambient import (
detect_buildkite,
detect_circleci,
detect_gcp,
detect_github,
detect_gitlab,
)
detectors: list[Callable[..., str | None]] = [
detect_github,
detect_gcp,
detect_buildkite,
detect_gitlab,
detect_circleci,
]
for detector in detectors:
credential = detector(audience)
if credential is not None:
_validate_credential(credential, audience)
return credential
return None
def decode_oidc_token(token: str) -> tuple[str, str, str]:
# Split the token into its three parts: header, payload, and signature
header, payload, signature = token.split(".")
# Decode base64-encoded header and payload
decoded_header = base64.urlsafe_b64decode(header + "==").decode("utf-8")
decoded_payload = base64.urlsafe_b64decode(payload + "==").decode("utf-8")
return decoded_header, decoded_payload, signature
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