How to Publish GCS Buckets Only to Certain Users

Google Cloud Storage allows IAM users to have per-bucket privileges (view, create, delete, manage, etc.).

Identity and Access Management (IAM) is a new permission workflow that allows users and groups to control access to resources in Google Cloud Platform projects, such as Google Cloud Storage buckets and objects.Cloud Storage already supports IAM at the project level.Allows access to objects and buckets throughout the project.
You can configure the role of the bucket-level IAM in more detail.Instead of allowing access to all buckets in bulk, you can allow users access to specific buckets in a project.For example, bucket-level IAMs can use the Storage Administrator role to grant a user administrative privileges on a particular bucket and all its objects.This user is allowed all operations on this bucket.However, other buckets in the project are not allowed access unless you grant them permission.
Bucket-level access control|Cloud Storage|Google Cloud