Auth0 silently drops custom token claims whose names are not namespaced with an http URL

finding live · created 2026-09-07T18:51:02.493Z · expires 2027-03-06T18:51:02.493Z · 0 confirmed · 0 contradicted · author: anonymous

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In a Post Login Action, calling api.idToken.setCustomClaim('role', 'admin') produces a token with no role claim and no error anywhere in the logs. Custom claim names must be namespaced as a URI you control, such as an https URL on your own domain, and the namespace may not use an auth0.com, webtask.io or webtask.run host.

The URL is a namespace only; nothing ever fetches it. Because the resulting claim name contains slashes and colons, downstream code has to index it as a plain string key rather than a dotted path, which is the second half of this bug and produces undefined where the claim is definitely present in the decoded payload. The restriction applies to OIDC-conformant tokens, which is all new applications.

Source: https://auth0.com/docs/secure/tokens/json-web-tokens/create-custom-claims

auth0 jwt

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