Behavior: Fetches the content definition schema for the given ID. A security check is performed to verify the caller has permission to access this content definition. Content definitions describe the structure and fields of a content type in the system.

Authorization: Requires a valid Bearer token. The caller must also have permission to access the requested content definition.

Side Effects: None.

Error Scenarios: Returns 404 if no content definition exists with the specified ID. Returns 400 if the caller does not have permission to access the content definition.