You have a storage account named storage1 and two web apps named app1 and app2. Both apps will write data to storage1. Ensure that each app can read only the data it has written. What should you do?

The correct answer ensures data isolation and confidentiality. By providing each app with a unique encryption key, only the app possessing that specific key can decrypt and read the data it encrypted. This directly addresses the requirement that "each app can read only the data it has written." The other options are incorrect because they do not guarantee this specific level of data isolation. Using system-assigned or user-managed identities with Azure AD authentication primarily controls access to the storage account itself, not granular access to specific data within it based on who wrote it. While you can assign roles, these roles typically grant broader permissions (e.g., "Storage Blob Data Contributor") rather than restricting read access to only self-written data. Using separate storage account keys would grant full access to the entire storage account to each app, violating the "read only the data it has written" requirement.