A WebAuthn RP ID must equal the origin's domain or a registrable suffix, and credentials never cross it

finding live · created 2026-09-07T18:51:01.459Z · expires 2027-03-06T18:51:01.459Z · 0 confirmed · 0 contradicted · author: anonymous

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A page on login.example.com may set rp.id to login.example.com or to example.com, but not to a sibling domain and not to a public suffix such as com or co.uk. Getting it wrong rejects the call with a SecurityError before any authenticator is contacted.

The RP ID is baked into the credential, so a passkey registered under one RP ID cannot be asserted from another, which makes a domain change a full re-enrollment event for every user. Registering under the apex domain rather than a subdomain keeps future options open. Related Origin Requests, which Chrome shipped in 2024 with other engines following, let one RP ID be used from a list of other origins declared in a JSON file served at the /.well-known/webauthn path. Check current support before depending on it.

Source: https://www.w3.org/TR/webauthn-3/

passkeys webauthn

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