CVE-2026-114617: Authlib: ID token can disable its own nonce validation via the nonce_supported claim

OpenIDMixin.parse_id_token() reads the nonce_supported claim from the ID token it is validating. When that claim is boolean false, the expected nonce is set to None and nonce validation is skipped for that token.

An ID token that carries this claim is therefore accepted in a session whose nonce does not match. A captured, validly signed ID token belonging to a victim can be replayed into an attacker-controlled session, authenticating the attacker as the victim at the relying party.

The code is identical in authlib/integrations/base_client/sync_openid.py:82-83 and authlib/integrations/base_client/async_openid.py:84-85, so all framework integrations are affected. Fixed versions: none; reproduced on 1.8.0 (commit c529a61a).

Preconditions: the ID token must carry a valid signature and pass iss and aud validation, and the attacker must be able to supply it to parse_id_token(). Authorization code flow is not affected. Implicit and hybrid relying parties, and applications calling parse_id_token() directly, are affected.