fix(consent): allow IdP origin in CSP form-action for Chromium#33
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The consent page CSP set `form-action 'self'`, which Chromium enforces against every URL in the redirect chain initiated by a form submit (CSP3 §6.5). The approve POST 302s to the upstream IdP, so Chrome / Edge / Brave / Opera blocked the navigation client-side and /callback never fired. Firefox and Safari work because they check only the immediate action= URL. Derive the upstream authorize endpoint's origin once at handler construction from oauth2Cfg.Endpoint.AuthURL (already populated by OIDC discovery — no new config required for the common case), lower- case it per CSP3 §6.7.2.5, and append to the form-action source list. Skip the precompute + warn when RenderConsentPage=false. Add CSP_FORM_ACTION_EXTRA for IdP topologies whose redirect chain crosses the authorize host (Entra B2C, federated AD FS, personal Microsoft accounts, sovereign clouds). Entries are validated against the CSP3 §2.4 host-source ABNF — stricter than RFC 3986 reg-name so sub-delims (`;`, `,`, `&`, `_`) that would break out of the directive when emitted are rejected at startup.
This was referenced May 28, 2026
babs
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Jun 4, 2026
Chromium enforces the consent page's form-action directive against every hop of the redirect chain a form submit initiates. Client-side hops after redirect_uri (e.g. Power Platform's global.consent.azure-apim.net -> regional UI origin) are unknowable in advance, so origin enumeration (#33 IdP extras, #35 redirect_uri) could never be complete. - answer POST /consent (approve/deny/server-error) with a 200 same-origin interstitial (meta refresh, no JS) instead of a 302; form navigation ends at the proxy, downstream hops are a regular navigation that form-action does not govern - tighten consent page CSP to form-action 'self'; drop buildConsentCSPSources/formatConsentCSP and per-render widening - deprecate CSP_FORM_ACTION_EXTRA (parsed, ignored, startup warn) - re-render consent page with fresh JTI on replayed submit instead of a dead-end 400 consent_replay; decision still requires a new explicit click, single-use guarantee unchanged
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The consent page CSP set
form-action 'self', which Chromium enforces against every URL in the redirect chain initiated by a form submit (CSP3 §6.5). The approve POST 302s to the upstream IdP, so Chrome / Edge / Brave / Opera blocked the navigation client-side and /callback never fired. Firefox and Safari work because they check only the immediate action= URL.Derive the upstream authorize endpoint's origin once at handler construction from oauth2Cfg.Endpoint.AuthURL (already populated by OIDC discovery — no new config required for the common case), lower- case it per CSP3 §6.7.2.5, and append to the form-action source list. Skip the precompute + warn when RenderConsentPage=false.
Add CSP_FORM_ACTION_EXTRA for IdP topologies whose redirect chain crosses the authorize host (Entra B2C, federated AD FS, personal Microsoft accounts, sovereign clouds). Entries are validated against the CSP3 §2.4 host-source ABNF — stricter than RFC 3986 reg-name so sub-delims (
;,,,&,_) that would break out of the directive when emitted are rejected at startup.