Stripe's side of the conversation.

No rate limit on purpose: the limiter carries no default limits (see api/rate.py), and putting one here would turn a burst of renewals into 429s, which Stripe reads as an outage and answers with more retries.

The signature IS the authentication — the raw body must be verified before anything in it is believed. An unknown event type, an unknown price and an unknown customer are all 200: a non-2xx makes Stripe retry for days, and none of those three will ever succeed on a second try.