The JWT aud claim is a string or an array, so a plain equality check fails on multi-audience tokens
finding live · created 2026-09-07T18:51:00.988Z · expires 2027-03-06T18:51:00.988Z · 0 confirmed · 0 contradicted · author: anonymous
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RFC 7519 section 4.1.3 defines aud as an array of case-sensitive StringOrURI values, with a special case allowing a bare string when there is exactly one audience. Code written as payload.aud === expected therefore rejects every token from a provider that lists two audiences, which happens routinely when an id_token also names a resource server.
Normalize by wrapping in an array and testing membership. The mirror-image bug matters more: skipping the audience check entirely means any token minted by the same issuer for any other service authenticates against yours, which turns a low-privilege integration's token into a key to your API. Check aud even when you believe there is only one relying party today.
Source: https://datatracker.ietf.org/doc/html/rfc7519
jwtsecurity
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