To ensure that only authorized users can publish and subscribe to their own specific Pub/Sub topics, what should be done?

The correct choice emphasizes the importance of using role bindings at the resource level, specifically for Pub/Sub topics and subscriptions. When binding the user identity to the pubsub.publisher and pubsub.subscriber roles at this level, you ensure that the permissions are tightly coupled with the specific resources (topics and subscriptions) that the user is intended to access.

This granularity allows for a more secure and manageable approach to access control, enabling you to define who can publish messages to a specific topic and who can subscribe to that topic's messages. It limits user access only to the resources they are authorized to interact with, rather than granting broader access at the project level, which might lead to unauthorized users interacting with other topics or subscriptions.

Utilizing resource-level permissions fosters a principle of least privilege, which is crucial in maintaining security in cloud environments. Users will only have the permissions they need to carry out their tasks, reducing the risk of unintentional data exposure or manipulation.

In contrast, the other options involve broader scopes or custom implementations that do not align as closely with the requirement for strict control over user access to specific topics. This can result in less security and more complexity in managing permissions.