Restrict REST API to Logged-In Users

How can you restrict rest api to logged-in users in WordPress? This use case shows how a focused WordPress code snippet can handle the task without installing a heavy plugin. The snippet should require login for REST API access and produce this result: Unauthenticated REST API requests return an authorization error. You can also log in to LeonLab.ai, describe this WordPress use case in plain English, generate the snippet, review the PHP code, and deploy it to the selected WordPress project.