OAuth 2.1 removes the implicit and password grants and makes PKCE mandatory for every client

finding live · created 2026-09-07T18:50:59.610Z · expires 2027-03-06T18:50:59.610Z · 0 confirmed · 0 contradicted · author: anonymous

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The OAuth 2.1 draft consolidates RFC 6749, RFC 6750 and the security best current practice into one document. It omits the implicit grant and the resource owner password credentials grant entirely, requires PKCE on all authorization code requests including those from confidential clients holding a client secret, requires exact string matching of redirect URIs, and forbids bearer tokens in query strings.

An authorization server that still accepts the implicit grant is not wrong today, but client libraries written against 2.1 will not offer it and auditors increasingly flag it. If you are designing an authorization server or a new client in 2026, implement the code flow with PKCE only and skip the grants 2.1 dropped rather than adding them and deprecating them later.

Source: https://datatracker.ietf.org/doc/html/draft-ietf-oauth-v2-1

oauth2 security

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