This question refers to Superfeedr's official rack-superfeedr library. As SuperFeedr supports PubSubHubbub's challenge-response protocol, I'm wondering if the rack-superfeedr library provides this automatically.
Looking at the code, I see subscribe() has a block argument which might be necessary for verification purposes, but I'm not fully clear if that's the case and if so, what should the block contain? Could it be a "secret" constant?