Aug
05
2023

Impersonating a Google Cloud Service Account

Impersonating a Google Cloud service account means assuming the identity of the service account to perform actions on behalf of that account. This can be useful in scenarios where you want to delegate permissions or perform operations as the service account. There are a few ways to achieve this.

GCP SA Impersonation

1. Application Default Credentials (ADC)

Google Cloud SDK and Google Cloud Client Libraries use ADC by default. ADC automatically provides the necessary credentials based on the environment where your code is running, such as a Google Cloud service like Compute Engine, App Engine, or Google Kubernetes Engine. In these environments, you can simply specify the service account email when configuring the environment, and the credentials will be automatically used.

2. Service Account Key File

You can create a service account key file (.json) from the Google Cloud Console. This key file contains the necessary credentials to authenticate as the service account. You can then use this key file to impersonate the service account by setting the `GOOGLE_APPLICATION_CREDENTIALS` environment variable to the path of the key file.

import os
from google. Cloud import storage

# Set the path to the service account key file
os.environ['GOOGLE_APPLICATION_CREDENTIALS'] = '/path/to/service-account-key.json'

# Create a client using the impersonated service account credentials
client = storage.Client()

# Use the client to perform actions as the service account
# For example, list buckets
buckets = list(client.list_buckets())

3. Google Cloud IAM Session Tokens

Google Cloud IAM Session Tokens allow you to generate short-lived credentials that can be used to impersonate a service account programmatically. You can use the `google.auth` library to obtain a session token by specifying the target service account email.

from google.auth import impersonated_credentials
from google.auth.transport import requests

target_principal = '[email protected]'

# Impersonate the service account and generate a session token
source_credentials, target_principal_credentials = impersonated_credentials.Credentials(
source_credentials=your_credentials,
target_principal=target_principal,
target_scopes=['https://www.googleapis.com/auth/cloud-platform']
).refresh(requests.Request())

# Use the session token to authenticate as the service account
# For example, using the Google Cloud Storage client library
from google.cloud import storage

client = storage.Client(credentials=target_principal_credentials)

# Perform actions as the impersonated service account
buckets = list(client.list_buckets())

These are some of the common ways to impersonate a Google Cloud service account in Python. Choose the method that best fits your use case based on your environment and requirements.

GCP SA Role Assignment

To impersonate a Google Cloud service account, you need to assign a role that grants the necessary permissions to the account performing the impersonation. The specific role required depends on the actions you want to perform on behalf of the service account. Here are some roles commonly used for impersonation:

1. Service Account User (`roles/iam.serviceAccountUser`)

This role allows the account to act as the service account and perform actions on its behalf. It provides broad access to resources associated with the service account, including calling Google Cloud APIs.

2. Service Account Token Creator (`roles/iam.serviceAccountTokenCreator`)

This role allows the account to generate short-lived authentication tokens for the service account. It can be used when using Google Cloud IAM Session Tokens for impersonation.

3. Specific Roles

In addition to the above roles, you can assign more specific roles based on the services and resources you want to access. For example, if you want to impersonate a service account to read and write data in Google Cloud Storage, you can assign the `roles/storage.objectViewer` or `roles/storage.objectCreator` roles to the impersonating account.

It’s important to assign the least privileged roles necessary for the specific actions you need to perform. Granting excessive permissions through overly permissive roles can introduce security risks. Additionally, always follow the principle of least privilege and regularly review and adjust the roles assigned to your accounts to ensure they align with your requirements and security best practices.

You can assign roles using the Google Cloud Console, the Cloud SDK’s `gcloud` command-line tool, or programmatically via the Google Cloud IAM API or the Cloud IAM client libraries.