---
phase: 08-social-sign-in
plan: 02
subsystem: auth-oauth
tags: [google, oauth2, oidc, sessions]
requires:
  - phase: 08-social-sign-in
    provides: nullable users and user_identities
provides:
  - Google OAuth start and callback routes
  - OAuth state and nonce cookies
  - mockable token exchange and ID token verifier interfaces
affects: [auth-ui, apple-sign-in, account-providers]
tech-stack:
  added: [golang.org/x/oauth2, github.com/coreos/go-oidc/v3/oidc]
  patterns: [provider verifier interface, transaction account linking]
key-files:
  created:
    - backend/internal/auth/oauth.go
    - backend/internal/auth/oauth_test.go
    - backend/internal/web/handlers_social.go
    - backend/internal/web/handlers_social_test.go
  modified:
    - backend/cmd/web/main.go
    - backend/internal/web/handlers_auth.go
    - backend/internal/web/router.go
    - backend/go.mod
    - backend/go.sum
key-decisions:
  - "Google provider tokens are verification evidence only; Xtablo still issues the local session cookie."
  - "Provider subject wins after link; email conflicts update identity metadata without relinking."
patterns-established:
  - "OAuth handlers depend on fakeable CodeExchanger and IDTokenVerifier interfaces."
requirements-completed: [AUTH-08, AUTH-09, AUTH-12, AUTH-13]
duration: 35min
completed: 2026-05-15
---

# Phase 8 Plan 02: Google Social Sign-in Summary

**Google OAuth/OIDC sign-in with state and nonce cookies, verified-email linking, and local Xtablo session issuance**

## Performance

- **Duration:** ~35 min
- **Started:** 2026-05-15T19:16:00Z
- **Completed:** 2026-05-15T19:51:00Z
- **Tasks:** 2
- **Files modified:** 9

## Accomplishments

- Added Google provider config and env wiring.
- Added OAuth state/nonce cookie helpers and OIDC verifier support.
- Added `/auth/google/start` and `/auth/google/callback`.
- Added tests for start redirect, invalid state, unverified email, verified linking, social-only creation, subject precedence, and conflict handling.

## Task Commits

1. **Google social sign-in flow** - `6779663` (`feat(08-02)`)

## Deviations from Plan

Combined Google primitives and handler wiring into one production commit because the handler tests compile against the newly introduced auth interfaces.

**Total deviations:** 1 process deviation. **Impact:** No functional scope change.

## Issues Encountered

DB-backed linking tests skip locally without `TEST_DATABASE_URL`; non-DB OAuth tests run in the default suite.

## User Setup Required

Google OAuth credentials are documented in Plan 05 docs.

## Next Phase Readiness

Apple can reuse the same provider claim and account-linking machinery.

