# Copyright 2018 Google Inc.
#
# 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.
"""Google Cloud Impersonated credentials.
This module provides authentication for applications where local credentials
impersonates a remote service account using `IAM Credentials API`_.
This class can be used to impersonate a service account as long as the original
Credential object has the "Service Account Token Creator" role on the target
service account.
.. _IAM Credentials API:
https://cloud.google.com/iam/credentials/reference/rest/
"""
import base64
import copy
from datetime import datetime
import json
import six
from six.moves import http_client
from google.auth import _helpers
from google.auth import credentials
from google.auth import exceptions
from google.auth import jwt
from google.auth.transport.requests import AuthorizedSession
_DEFAULT_TOKEN_LIFETIME_SECS = 3600 # 1 hour in seconds
_IAM_SCOPE = ["https://www.googleapis.com/auth/iam"]
_IAM_ENDPOINT = (
"https://iamcredentials.googleapis.com/v1/projects/-"
+ "/serviceAccounts/{}:generateAccessToken"
)
_IAM_SIGN_ENDPOINT = (
"https://iamcredentials.googleapis.com/v1/projects/-"
+ "/serviceAccounts/{}:signBlob"
)
_IAM_IDTOKEN_ENDPOINT = (
"https://iamcredentials.googleapis.com/v1/"
+ "projects/-/serviceAccounts/{}:generateIdToken"
)
_REFRESH_ERROR = "Unable to acquire impersonated credentials"
_DEFAULT_TOKEN_LIFETIME_SECS = 3600 # 1 hour in seconds
_DEFAULT_TOKEN_URI = "https://oauth2.googleapis.com/token"
def _make_iam_token_request(request, principal, headers, body):
"""Makes a request to the Google Cloud IAM service for an access token.
Args:
request (Request): The Request object to use.
principal (str): The principal to request an access token for.
headers (Mapping[str, str]): Map of headers to transmit.
body (Mapping[str, str]): JSON Payload body for the iamcredentials
API call.
Raises:
TransportError: Raised if there is an underlying HTTP connection
Error
DefaultCredentialsError: Raised if the impersonated credentials
are not available. Common reasons are
`iamcredentials.googleapis.com` is not enabled or the
`Service Account Token Creator` is not assigned
"""
iam_endpoint = _IAM_ENDPOINT.format(principal)
body = json.dumps(body).encode("utf-8")
response = request(url=iam_endpoint, method="POST", headers=headers, body=body)
response_body = response.data.decode("utf-8")
if response.status != http_client.OK:
exceptions.RefreshError(_REFRESH_ERROR, response_body)
try:
token_response = json.loads(response.data.decode("utf-8"))
token = token_response["accessToken"]
expiry = datetime.strptime(token_response["expireTime"], "%Y-%m-%dT%H:%M:%SZ")
return token, expiry
except (KeyError, ValueError) as caught_exc:
new_exc = exceptions.RefreshError(
"{}: No access token or invalid expiration in response.".format(
_REFRESH_ERROR
),
response_body,
)
six.raise_from(new_exc, caught_exc)
[docs]class Credentials(credentials.Credentials, credentials.Signing):
"""This module defines impersonated credentials which are essentially
impersonated identities.
Impersonated Credentials allows credentials issued to a user or
service account to impersonate another. The target service account must
grant the originating credential principal the
`Service Account Token Creator`_ IAM role:
For more information about Token Creator IAM role and
IAMCredentials API, see
`Creating Short-Lived Service Account Credentials`_.
.. _Service Account Token Creator:
https://cloud.google.com/iam/docs/service-accounts#the_service_account_token_creator_role
.. _Creating Short-Lived Service Account Credentials:
https://cloud.google.com/iam/docs/creating-short-lived-service-account-credentials
Usage:
First grant source_credentials the `Service Account Token Creator`
role on the target account to impersonate. In this example, the
service account represented by svc_account.json has the
token creator role on
`impersonated-account@_project_.iam.gserviceaccount.com`.
Enable the IAMCredentials API on the source project:
`gcloud services enable iamcredentials.googleapis.com`.
Initialize a source credential which does not have access to
list bucket::
from google.oauth2 import service_acccount
target_scopes = [
'https://www.googleapis.com/auth/devstorage.read_only']
source_credentials = (
service_account.Credentials.from_service_account_file(
'/path/to/svc_account.json',
scopes=target_scopes))
Now use the source credentials to acquire credentials to impersonate
another service account::
from google.auth import impersonated_credentials
target_credentials = impersonated_credentials.Credentials(
source_credentials=source_credentials,
target_principal='impersonated-account@_project_.iam.gserviceaccount.com',
target_scopes = target_scopes,
lifetime=500)
Resource access is granted::
client = storage.Client(credentials=target_credentials)
buckets = client.list_buckets(project='your_project')
for bucket in buckets:
print(bucket.name)
"""
def __init__(
self,
source_credentials,
target_principal,
target_scopes,
delegates=None,
lifetime=_DEFAULT_TOKEN_LIFETIME_SECS,
):
"""
Args:
source_credentials (google.auth.Credentials): The source credential
used as to acquire the impersonated credentials.
target_principal (str): The service account to impersonate.
target_scopes (Sequence[str]): Scopes to request during the
authorization grant.
delegates (Sequence[str]): The chained list of delegates required
to grant the final access_token. If set, the sequence of
identities must have "Service Account Token Creator" capability
granted to the prceeding identity. For example, if set to
[serviceAccountB, serviceAccountC], the source_credential
must have the Token Creator role on serviceAccountB.
serviceAccountB must have the Token Creator on
serviceAccountC.
Finally, C must have Token Creator on target_principal.
If left unset, source_credential must have that role on
target_principal.
lifetime (int): Number of seconds the delegated credential should
be valid for (upto 3600).
"""
super(Credentials, self).__init__()
self._source_credentials = copy.copy(source_credentials)
# Service account source credentials must have the _IAM_SCOPE
# added to refresh correctly. User credentials cannot have
# their original scopes modified.
if isinstance(self._source_credentials, credentials.Scoped):
self._source_credentials = self._source_credentials.with_scopes(_IAM_SCOPE)
self._target_principal = target_principal
self._target_scopes = target_scopes
self._delegates = delegates
self._lifetime = lifetime
self.token = None
self.expiry = _helpers.utcnow()
[docs] @_helpers.copy_docstring(credentials.Credentials)
def refresh(self, request):
self._update_token(request)
@property
def expired(self):
return _helpers.utcnow() >= self.expiry
def _update_token(self, request):
"""Updates credentials with a new access_token representing
the impersonated account.
Args:
request (google.auth.transport.requests.Request): Request object
to use for refreshing credentials.
"""
# Refresh our source credentials.
self._source_credentials.refresh(request)
body = {
"delegates": self._delegates,
"scope": self._target_scopes,
"lifetime": str(self._lifetime) + "s",
}
headers = {"Content-Type": "application/json"}
# Apply the source credentials authentication info.
self._source_credentials.apply(headers)
self.token, self.expiry = _make_iam_token_request(
request=request,
principal=self._target_principal,
headers=headers,
body=body,
)
[docs] def sign_bytes(self, message):
iam_sign_endpoint = _IAM_SIGN_ENDPOINT.format(self._target_principal)
body = {"payload": base64.b64encode(message), "delegates": self._delegates}
headers = {"Content-Type": "application/json"}
authed_session = AuthorizedSession(self._source_credentials)
response = authed_session.post(
url=iam_sign_endpoint, headers=headers, json=body
)
return base64.b64decode(response.json()["signedBlob"])
@property
def signer_email(self):
return self._target_principal
@property
def service_account_email(self):
return self._target_principal
@property
def signer(self):
return self
[docs]class IDTokenCredentials(credentials.Credentials):
"""Open ID Connect ID Token-based service account credentials.
"""
def __init__(self, target_credentials, target_audience=None, include_email=False):
"""
Args:
target_credentials (google.auth.Credentials): The target
credential used as to acquire the id tokens for.
target_audience (string): Audience to issue the token for.
include_email (bool): Include email in IdToken
"""
super(IDTokenCredentials, self).__init__()
if not isinstance(target_credentials, Credentials):
raise exceptions.GoogleAuthError(
"Provided Credential must be " "impersonated_credentials"
)
self._target_credentials = target_credentials
self._target_audience = target_audience
self._include_email = include_email
def from_credentials(self, target_credentials, target_audience=None):
return self.__class__(
target_credentials=self._target_credentials, target_audience=target_audience
)
def with_target_audience(self, target_audience):
return self.__class__(
target_credentials=self._target_credentials, target_audience=target_audience
)
def with_include_email(self, include_email):
return self.__class__(
target_credentials=self._target_credentials,
target_audience=self._target_audience,
include_email=include_email,
)
[docs] @_helpers.copy_docstring(credentials.Credentials)
def refresh(self, request):
iam_sign_endpoint = _IAM_IDTOKEN_ENDPOINT.format(
self._target_credentials.signer_email
)
body = {
"audience": self._target_audience,
"delegates": self._target_credentials._delegates,
"includeEmail": self._include_email,
}
headers = {"Content-Type": "application/json"}
authed_session = AuthorizedSession(self._target_credentials._source_credentials)
response = authed_session.post(
url=iam_sign_endpoint,
headers=headers,
data=json.dumps(body).encode("utf-8"),
)
id_token = response.json()["token"]
self.token = id_token
self.expiry = datetime.fromtimestamp(jwt.decode(id_token, verify=False)["exp"])
