Glossary
Idempotency Key
An idempotency key is a unique value the client generates and attaches to a request, so that if the request has to be resent — because a network failure left the client uncertain whether the first attempt succeeded — the receiving system can recognize the retry as the same logical request rather than a new one. The action executes once; the retry simply returns the original result rather than triggering the effect a second time.
This matters for authorization specifically wherever the action being retried is consequential: a payment, an irreversible state change. Without an idempotency key, a client's honest attempt to recover from an uncertain failure — retry, just in case the first attempt didn't go through — can end up authorizing the same action twice, purely as a side effect of ordinary network unreliability rather than anything the requester actually intended.