OIDC deployments cannot authorize a third-party application: the device grant is accounts-only (#81)

[jan21deepak]

Opened automatically by Cursor Forge as a same-repo PR on jan21deepak/omnigent
after the Cloud Agent pushed cursor/oidc-device-grant-7cd5 (not against an upstream parent).

Fixes #81.

Cursor agent: bc-ef0ddc19-7ffa-49f6-b9d2-ea207bc27cd5

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Note

High Risk
Changes authentication consent gating, OIDC login/callback behavior, and session JWT claims—security-sensitive paths where a mistake could weaken device-grant phishing defenses or break OIDC logins.

Overview
Enables the RFC 8628 device grant on OIDC deployments (still opt-in via OMNIGENT_DEVICE_GRANT_ENABLED), so external clients can get scoped delegated tokens—not only accounts mode. First-party CLI/Slack keep using cli-login on OIDC; the design doc calls that out.

Consent anti-phishing is tightened for OIDC. The device consent page no longer trusts session iat (IdP silent SSO can mint a “fresh” cookie without user action). Sessions now carry optional auth_time when credentials were actually verified; accounts logins set it on password/magic/setup; OIDC sets it only when the IdP attests a fresh login via verified id_token auth_time. Consent requires auth_time ≥ grant.created_at. Every login bounce from consent uses reauth=1; OIDC /auth/login forwards that as prompt=login + max_age=0, and the callback 403s if a forced re-auth was requested but the IdP reused a session.

Mount policy and operator UX: unsupported_reason blocks header mode (no mintable session) and non-OIDC providers like GitHub (no prompt/auth_time). app.py evaluates this before the auth-router block so header-mode operators get a warning when the flag is set but /oauth/* cannot mount. return_to on consent bounces is URL-encoded so odd user_code values don’t break the round-trip.

Tests cover OIDC mount, GitHub refusal, reauth prompt forwarding, callback verification, and consent with proven vs unproven cookies.

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[jan21deepak]

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