267 lines
9 KiB
Python
267 lines
9 KiB
Python
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# Copyright 2016 Google LLC
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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"""Google ID Token helpers.
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Provides support for verifying `OpenID Connect ID Tokens`_, especially ones
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generated by Google infrastructure.
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To parse and verify an ID Token issued by Google's OAuth 2.0 authorization
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server use :func:`verify_oauth2_token`. To verify an ID Token issued by
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Firebase, use :func:`verify_firebase_token`.
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A general purpose ID Token verifier is available as :func:`verify_token`.
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Example::
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from google.oauth2 import id_token
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from google.auth.transport import requests
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request = requests.Request()
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id_info = id_token.verify_oauth2_token(
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token, request, 'my-client-id.example.com')
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if id_info['iss'] != 'https://accounts.google.com':
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raise ValueError('Wrong issuer.')
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userid = id_info['sub']
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By default, this will re-fetch certificates for each verification. Because
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Google's public keys are only changed infrequently (on the order of once per
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day), you may wish to take advantage of caching to reduce latency and the
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potential for network errors. This can be accomplished using an external
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library like `CacheControl`_ to create a cache-aware
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:class:`google.auth.transport.Request`::
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import cachecontrol
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import google.auth.transport.requests
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import requests
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session = requests.session()
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cached_session = cachecontrol.CacheControl(session)
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request = google.auth.transport.requests.Request(session=cached_session)
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.. _OpenID Connect ID Token:
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http://openid.net/specs/openid-connect-core-1_0.html#IDToken
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.. _CacheControl: https://cachecontrol.readthedocs.io
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"""
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import json
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import os
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import six
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from six.moves import http_client
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from google.auth import environment_vars
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from google.auth import exceptions
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from google.auth import jwt
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# The URL that provides public certificates for verifying ID tokens issued
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# by Google's OAuth 2.0 authorization server.
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_GOOGLE_OAUTH2_CERTS_URL = "https://www.googleapis.com/oauth2/v1/certs"
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# The URL that provides public certificates for verifying ID tokens issued
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# by Firebase and the Google APIs infrastructure
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_GOOGLE_APIS_CERTS_URL = (
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"https://www.googleapis.com/robot/v1/metadata/x509"
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"/securetoken@system.gserviceaccount.com"
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)
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_GOOGLE_ISSUERS = ["accounts.google.com", "https://accounts.google.com"]
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def _fetch_certs(request, certs_url):
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"""Fetches certificates.
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Google-style cerificate endpoints return JSON in the format of
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``{'key id': 'x509 certificate'}``.
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Args:
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request (google.auth.transport.Request): The object used to make
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HTTP requests.
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certs_url (str): The certificate endpoint URL.
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Returns:
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Mapping[str, str]: A mapping of public key ID to x.509 certificate
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data.
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"""
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response = request(certs_url, method="GET")
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if response.status != http_client.OK:
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raise exceptions.TransportError(
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"Could not fetch certificates at {}".format(certs_url)
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)
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return json.loads(response.data.decode("utf-8"))
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def verify_token(id_token, request, audience=None, certs_url=_GOOGLE_OAUTH2_CERTS_URL):
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"""Verifies an ID token and returns the decoded token.
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Args:
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id_token (Union[str, bytes]): The encoded token.
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request (google.auth.transport.Request): The object used to make
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HTTP requests.
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audience (str): The audience that this token is intended for. If None
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then the audience is not verified.
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certs_url (str): The URL that specifies the certificates to use to
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verify the token. This URL should return JSON in the format of
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``{'key id': 'x509 certificate'}``.
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Returns:
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Mapping[str, Any]: The decoded token.
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"""
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certs = _fetch_certs(request, certs_url)
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return jwt.decode(id_token, certs=certs, audience=audience)
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def verify_oauth2_token(id_token, request, audience=None):
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"""Verifies an ID Token issued by Google's OAuth 2.0 authorization server.
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Args:
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id_token (Union[str, bytes]): The encoded token.
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request (google.auth.transport.Request): The object used to make
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HTTP requests.
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audience (str): The audience that this token is intended for. This is
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typically your application's OAuth 2.0 client ID. If None then the
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audience is not verified.
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Returns:
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Mapping[str, Any]: The decoded token.
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Raises:
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exceptions.GoogleAuthError: If the issuer is invalid.
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"""
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idinfo = verify_token(
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id_token, request, audience=audience, certs_url=_GOOGLE_OAUTH2_CERTS_URL
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)
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if idinfo["iss"] not in _GOOGLE_ISSUERS:
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raise exceptions.GoogleAuthError(
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"Wrong issuer. 'iss' should be one of the following: {}".format(
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_GOOGLE_ISSUERS
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)
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)
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return idinfo
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def verify_firebase_token(id_token, request, audience=None):
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"""Verifies an ID Token issued by Firebase Authentication.
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Args:
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id_token (Union[str, bytes]): The encoded token.
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request (google.auth.transport.Request): The object used to make
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HTTP requests.
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audience (str): The audience that this token is intended for. This is
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typically your Firebase application ID. If None then the audience
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is not verified.
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Returns:
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Mapping[str, Any]: The decoded token.
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"""
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return verify_token(
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id_token, request, audience=audience, certs_url=_GOOGLE_APIS_CERTS_URL
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)
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def fetch_id_token(request, audience):
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"""Fetch the ID Token from the current environment.
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This function acquires ID token from the environment in the following order:
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1. If the application is running in Compute Engine, App Engine or Cloud Run,
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then the ID token are obtained from the metadata server.
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2. If the environment variable ``GOOGLE_APPLICATION_CREDENTIALS`` is set
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to the path of a valid service account JSON file, then ID token is
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acquired using this service account credentials.
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3. If metadata server doesn't exist and no valid service account credentials
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are found, :class:`~google.auth.exceptions.DefaultCredentialsError` will
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be raised.
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Example::
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import google.oauth2.id_token
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import google.auth.transport.requests
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request = google.auth.transport.requests.Request()
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target_audience = "https://pubsub.googleapis.com"
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id_token = google.oauth2.id_token.fetch_id_token(request, target_audience)
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Args:
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request (google.auth.transport.Request): A callable used to make
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HTTP requests.
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audience (str): The audience that this ID token is intended for.
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Returns:
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str: The ID token.
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Raises:
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~google.auth.exceptions.DefaultCredentialsError:
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If metadata server doesn't exist and no valid service account
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credentials are found.
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"""
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# 1. First try to fetch ID token from metada server if it exists. The code
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# works for GAE and Cloud Run metadata server as well.
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try:
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from google.auth import compute_engine
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credentials = compute_engine.IDTokenCredentials(
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request, audience, use_metadata_identity_endpoint=True
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)
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credentials.refresh(request)
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return credentials.token
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except (ImportError, exceptions.TransportError, exceptions.RefreshError):
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pass
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# 2. Try to use service account credentials to get ID token.
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# Try to get credentials from the GOOGLE_APPLICATION_CREDENTIALS environment
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# variable.
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credentials_filename = os.environ.get(environment_vars.CREDENTIALS)
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if not (
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credentials_filename
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and os.path.exists(credentials_filename)
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and os.path.isfile(credentials_filename)
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):
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raise exceptions.DefaultCredentialsError(
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"Neither metadata server or valid service account credentials are found."
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)
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try:
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with open(credentials_filename, "r") as f:
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info = json.load(f)
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credentials_content = (
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(info.get("type") == "service_account") and info or None
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)
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from google.oauth2 import service_account
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credentials = service_account.IDTokenCredentials.from_service_account_info(
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credentials_content, target_audience=audience
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)
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except ValueError as caught_exc:
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new_exc = exceptions.DefaultCredentialsError(
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"Neither metadata server or valid service account credentials are found.",
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caught_exc,
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)
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six.raise_from(new_exc, caught_exc)
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credentials.refresh(request)
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return credentials.token
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