By "revocable, per-user keys" do you mean each user is given a unique URL to download premium content from or is some type of cryptographic DRM being leveraged?
back
2 comments
Yup; you get a URL to the premium feed with a unique hash on the end.
I'd imagine it's a token in the request headers
I doubt it's request headers since that would require the podcast player to set them. Putting it in the URL itself would make it work with every player on the planet.