Unit Tests / test (push) Successful in 10s
## Summary - Closes #24 (backend half) - Add `OAuthIdentity` model (provider + `sub`, access/refresh tokens) for SSO now and Drive reuse later (#11) - Endpoints: `GET /api/auth/oauth/<google|microsoft>/start/` and `/callback/` - Create or link `CustomUser` by verified email; issue same JWT access/refresh; redirect FE to `/auth/callback/` - Document `GOOGLE_OAUTH_*` / `MICROSOFT_OAUTH_*` / `OAUTH_CALLBACK_BASE_URL` in `.env.example` and `.env.prod.example` - Expose configured providers on `GET /api/public/settings/` as `oauth.google` / `oauth.microsoft` ## Pair with - Frontend PR: `chat_web_app` branch `feature/sso-oauth-24` ## Test plan - [ ] `python manage.py test chat_backend.tests.test_oauth` - [ ] With local Google/Microsoft client IDs set, complete start → IdP → callback → JWT redirect - [ ] Existing password user with same email links identity (no duplicate) - [ ] Unverified / missing email redirects with error code - [ ] Registration disabled: signup start 403; login without account → `account_not_found` - [ ] Secrets not committed; env examples onlyReviewed-on: #29