Make a Storage Bucket Public

The simplest way is to assign the AllUsers IAM role to the bucket. This makes it accessible for All users, regardless of their source.

What if I want to still block / restrict access to this bucket at a network level?

VPC Service Controls will help you define a perimeter around the bucket, so that only authorized perimeter bridge resources can access it.  More on VPC Service Controls

Summary

Cloud storage bucket has several access control mechanisms - including IAM, ACLs and VPC Service Controls.

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