How should you secure a Cloud Function that accesses other Google Cloud resources with the least privilege?

To secure a Cloud Function that needs to access other Google Cloud resources with the principle of least privilege, creating a custom IAM service account and allowing the deployer to act on its behalf is an effective strategy.

This approach ensures that the service account has specifically tailored permissions that only allow the necessary access to resources required for the Cloud Function's operation. By defining a custom IAM role, you can limit the permissions strictly to what the Cloud Function needs, thereby reducing the risk of unnecessary exposure or unauthorized access to other resources within your Google Cloud environment.

Moreover, by allowing the deployment service account to act on behalf of the custom IAM service account, you ensure that the operations performed by the Cloud Function are done securely and under a controlled identity. This adds an additional layer of security since actions are logged and can be traced back to a specific entity, reducing the surface area for potential vulnerabilities or misconfigurations.

The other choices involve broader permissions than necessary. Using an Editor role grants excessive access that goes against the principle of least privilege, which is crucial for maintaining secure and manageable cloud environments.