Add OIDC login and per-domain authorization

Authentication previously implied full authorization: any valid token
could manage every host, DNS provider, domain, and user. This adds SSO
login and a per-domain rights model.

OIDC login (authorization_code + PKCE):
- conf.oidc + conf.auth blocks; clientSecret in (gitignored) secrets.js.
- utils/oidc.js (state/PKCE, code exchange, userinfo) using global fetch.
- models/oidc_state.js: short-lived state store, auto-expiring via
  model-redis 1.5 per-key TTL.
- routes/auth.js: GET /auth/oidc/start + /auth/oidc/callback; JIT-provisions
  a local user, mints an AuthToken carrying the SSO groups, hands the token to
  the browser via a URL fragment. "Log in with SSO" button on the login page.

Authorization (groups + app overrides, per-domain, with ownership):
- models/grant.js + utils/roles.js (pure, unit-tested): effective rights from
  conf.auth (admin users/groups, group->role map), Grant records
  (user|group -> global|domain -> viewer|manager|admin), and ownership
  (created_by). Roles rank admin > manager(owner) > viewer.
- AuthToken stores session groups; middleware/auth.js exposes req.groups.
- middleware/authz.js: requireAdmin, requireDomainRole(minRole, resolveDomain),
  filterViewable. Applied across routes: host mutations need manager on the
  host's domain; reads are filtered to visible domains; DNS providers, user
  management, and grant management are global-admin-only; certs need viewer.
- routes/grant.js: admin CRUD for grants. Anti-lockout via conf.auth.adminUsers
  plus migrations/grant_bootstrap.js.

Frontend: /me returns effective rights; nav gates Users/Grants to admins;
grants management page; OIDC token-fragment handling in app-base.js.

Tests: utils/roles and utils/oidc unit-tested (no redis); wired into the test
scripts. Full suite 89 pass. Also verified end-to-end against redis (grant
resolution, middleware allow/deny/403, list filtering) and the OIDC pure flow.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

nodejs/views/top.ejs

@@ -51,11 +51,16 @@
 							DNS
 						</a>
 					</li>
-					<li class="nav-item">
+					<li class="nav-item nav-admin" style="display: none;">
 						<a class="nav-link" href="/users"><i class="fa-solid fa-users"></i>
 							Users
 						</a>
 					</li>
+					<li class="nav-item nav-admin" style="display: none;">
+						<a class="nav-link" href="/grants"><i class="fa-solid fa-user-shield"></i>
+							Grants
+						</a>
+					</li>
 					<li class="nav-item">
 						<a class="nav-link" href="https://github.com/theta42/proxy" target="_blank">
 							<i class="fa-brands fa-github"></i>
@@ -87,10 +92,13 @@
 					}
 				})
 
-				// Set the correct login/logout button
+				// Set the correct login/logout button, and reveal admin-only nav
+				// items for global admins.
 				app.auth.isLoggedIn(function(error, data){
 					if(data) $('#cl-logout-button').show();
 					else $('#cl-login-button').show();
+
+					if(data && data.isAdmin) $('.nav-admin').css('display', '');
 				});
 
 			});