Configuring Access and Security

The etag value enables optimistic concurrency control by ensuring that IAM policy updates only succeed if the policy hasn't been modified by another operation since it was retrieved.

Using etag for audit tracking is incorrect as audit logs have separate mechanisms. Etag doesn't verify integrity during replication as it changes with each policy modification. While etag does change when policies are updated, its primary purpose isn't timestamping but preventing concurrent modification conflicts.

Key concept: IAM policy concurrency control mechanisms.

The correct answer involves using the gcloud --impersonate-service-account flag or generating access tokens using the IAM credentials API to obtain short-lived credentials for the target service account.

When service account impersonation is properly configured (with the Service Account Token Creator role granted to the consultant's service account on the client's bq-admin service account), the consultant must actively invoke the impersonation mechanism to execute commands as the target service account.

There are two primary ways to do this:
1. Using the --impersonate-service-account flag with gcloud commands, for example: gcloud bq --impersonate-service-account=bq-admin@client-project.iam.gserviceaccount.com
2. Programmatically generating short-lived access tokens using the IAM credentials API (generateAccessToken method)

Both methods satisfy the requirement that audit logs show both identities - the original caller (consultant) and the impersonated service account (bq-admin).

The option suggesting downloading a service account key file is incorrect because it would bypass the impersonation requirement entirely. Using key files means the consultant would authenticate directly as the client's service account, and audit logs would not show the consultant's identity. Additionally, key files are a security risk and should be avoided.

The option about Workload Identity Federation pools is incorrect because Workload Identity Federation is designed for federating external identities (like AWS or Azure identities) into GCP, not for cross-project service account impersonation within GCP.

The option mentioning cross-project service account binding with Token Generator permissions describes granting the impersonation role (which the question states has already been done as a prerequisite), not the additional step needed to actually perform the impersonation. This is a necessary setup step but not the operational step required to execute commands.

To generate signed URLs using another service account's credentials, the batch processing service account needs the ability to create tokens on behalf of the reports service account. This requires the Service Account Token Creator role (roles/iam.serviceAccountTokenCreator).

When creating signed URLs, the process involves generating a signature using the private key of a service account. When one service account needs to sign URLs on behalf of another service account, it must be granted the Service Account Token Creator role on that target service account. This role grants the permission iam.serviceAccounts.signBlob, which is essential for creating signed URLs.

The correct configuration is to grant roles/iam.serviceAccountTokenCreator to the batch service account (sa-batch@analytics-proj.iam.gserviceaccount.com) on the reports service account resource (sa-reports@analytics-proj.iam.gserviceaccount.com). This allows the batch job to sign blobs and create signed URLs using the reports service account's identity.

The other options are incorrect for the following reasons:

• The Service Account User role (roles/iam.serviceAccountUser) allows a principal to run operations as the service account or attach it to resources, but it does not grant the ability to create tokens or sign blobs on behalf of that service account.

• Granting Storage Object Admin role at the project level would give the batch service account direct access to storage objects, but it wouldn't enable signing URLs using the reports service account's credentials. Cross-service authentication is also not a valid Google Cloud concept for this use case.

• The Service Account Key Admin role (roles/iam.serviceAccountKeyAdmin) allows managing service account keys (creating, deleting, listing keys), but it does not provide the ability to sign blobs or create tokens using the service account's credentials.