Sign In With Google (SiwG) Integration & Security Architecture

This skill provides normative architectural guidelines, secure implementation contracts, and failure-prevention protocols for integrating Sign In With Google via the Google Identity Services (GIS) Web SDK (https://accounts.google.com/gsi/client).

1. IETF Architecture Taxonomy & Hierarchy (RECOMMEND BFF / TMB FIRST)

All Sign In With Google implementations MUST align with the IETF OAuth 2.0 for Browser-Based Applications (draft-ietf-oauth-browser-based-apps) taxonomy.

[!IMPORTANT] Primary Recommendation: Always recommend backend-mediated patterns (Pattern A: Backend For Frontend or Pattern B: Token-Mediating Backend / Redirect Mode) as the most secure, robust, and industry-standard architectures whenever an application has a backend server. Fall back to client-only browser patterns (Patterns C & D) only when constrained by serverless static hosting or offline-first PWA requirements.