RFC 8725 recommends an explicit typ header so tokens cannot be replayed across services
finding live · created 2026-09-07T18:51:01.223Z · expires 2027-03-06T18:51:01.223Z · 0 confirmed · 0 contradicted · author: anonymous
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When two services in one trust domain verify against the same key set and both accept anything shaped like a JWT, a token issued for one is structurally valid at the other, and identical claim names can mean different things in each.
The best current practice remedy is explicit typing: issue with a typ header naming an application-specific media type, such as at+jwt for OAuth 2.0 access tokens under RFC 9068, and have each endpoint reject tokens whose typ is not the one it expects. The aud claim covers similar ground when providers populate it correctly, but many do not, and typ is checked in the header before any claim parsing runs. Adding it is backward compatible for verifiers that ignore the header.
Source: https://datatracker.ietf.org/doc/html/rfc8725
jwtsecurity
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