docs: update plans with Grafana OIDC progress

- auth-system-replacement.md: Mark OAuth2 client (Grafana) as completed,
  document key findings (PKCE, attribute paths, user requirements)
- monitoring-migration-victoriametrics.md: Note Grafana deployment on
  monitoring02 with Kanidm OIDC as test instance

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/plans/auth-system-replacement.md

@@ -151,11 +151,30 @@ Rationale:
 - Well above NixOS system users (typically <1000)
 - Avoids Podman/container issues with very high GIDs
 
+### Completed (2026-02-08) - OAuth2/OIDC for Grafana
+
+**OAuth2 client deployed for Grafana on monitoring02:**
+- Client ID: `grafana`
+- Redirect URL: `https://grafana-test.home.2rjus.net/login/generic_oauth`
+- Scope maps: `openid`, `profile`, `email`, `groups` for `users` group
+- Role mapping: `admins` group → Grafana Admin, others → Viewer
+
+**Configuration locations:**
+- Kanidm OAuth2 client: `services/kanidm/default.nix`
+- Grafana OIDC config: `services/grafana/default.nix`
+- Vault secret: `services/grafana/oauth2-client-secret`
+
+**Key findings:**
+- PKCE is required by Kanidm - enable `use_pkce = true` in Grafana
+- Must set `email_attribute_path`, `login_attribute_path`, `name_attribute_path` to extract from userinfo
+- Users need: primary credential (password + TOTP for MFA), membership in `users` group, email address set
+- Unix password is separate from primary credential (web login requires primary credential)
+
 ### Next Steps
 
 1. Enable PAM/NSS on production hosts (after test tier validation)
 2. Configure TrueNAS LDAP client for NAS integration testing
-3. Add OAuth2 clients (Grafana first)
+3. Add OAuth2 clients for other services as needed
 
 ## References