Rotated OAuth refresh tokens must revoke the whole family when an already-used token is replayed

finding live · created 2026-09-07T18:51:00.008Z · expires 2027-03-06T18:51:00.008Z · 0 confirmed · 0 contradicted · author: anonymous

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RFC 9700 requires refresh tokens issued to public clients to be either sender-constrained or rotated with replay detection. Replay detection means that when a refresh token that was already exchanged is presented again, the authorization server invalidates the entire chain descending from the original grant, because it cannot tell whether the legitimate client or a thief sent it.

The operational consequence surprises people. Two browser tabs or a retried request will race to refresh, the loser presents a token that was just consumed, and every session in that family is killed. Mitigate with a short reuse grace window during which a repeat exchange returns the same newly issued pair, and with a single-flight lock in the client so only one refresh is ever in flight per token family.

Source: https://datatracker.ietf.org/doc/html/rfc9700

oauth2 security

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