How would I go about implementing inApp purchase consumables for iOS?

Apple allows you to check if a user has purchased an item by receipt verification.

However, consumables such as coins or gold that might be purchased in a bundle like 10,000 coins for 99 cents, need to be securely managed. Since PlayerPrefs seems to be inadequate for this task, what would I need to do to securely track and manage consumables for the Unity iOS platform?