Possible security measures for in-app purchases downloaded from a server

I have an app I'm developing which relies开发者_如何学JAVA heavily on users being able to purchase content which will be downloaded from a server. As the app nears completion I'm becoming more concerned about my current distribution model, which is simply that when the user purchases an item the app then generates the correct URL and downloads the data (e.g., from www.website.com/content/music.mp3).

I have some simple web development experience, but I'm not aware of any authenticating process to ensure that only my iphone app has access to this content. In other words, as soon as somebody detects the outgoing URL request, they could get my content for free. Is there anything I can do to prevent, deter or even strongly discourage this?

Send the receipt to your server, verify the receipt and create a one-time-url for the file.