Phase 3 PR 28 — Admin UI cert-trust management page. New /certificates route (FleetAdmin-only) surfaces the OPC UA server's PKI store rejected + trusted certs and gives operators Trust / Delete / Revoke actions so rejected client certs can be promoted without touching disk. CertTrustService reads $PkiStoreRoot/{rejected,trusted}/certs/*.der files directly via X509CertificateLoader — no Opc.Ua dependency in the Admin project, which keeps the Admin host runnable on a machine that doesn't have the full Server install locally (only needs the shared PKI directory reachable; typical deployment has Admin + Server side-by-side on the same box and PkiStoreRoot defaults match so a plain-vanilla install needs no override). CertTrustOptions bound from the Admin's 'CertTrust:PkiStoreRoot' section, default %ProgramData%\OtOpcUa\pki (matches OpcUaServerOptions.PkiStoreRoot default). Trust action moves the .der from rejected/certs/ to trusted/certs/ via File.Move(overwrite:true) — idempotent, tolerates a concurrent operator doing the same move. Delete wipes the file. Revoke removes from trusted/certs/ (Opc.Ua re-reads the Directory store on each new client handshake, so no explicit reload signal is needed; operators retry the rejected connection after trusting). Thumbprint matching is case-insensitive because X509Certificate2.Thumbprint is upper-case hex but operators copy-paste from logs that sometimes lowercase it. Malformed files in the store are logged + skipped — a single bad .der can't take the whole management page offline. Missing store directories produce empty lists rather than exceptions so a pristine install (Server never run yet, no rejected/trusted dirs yet) doesn't crash the page.

Razor page layout: two tables (Rejected / Trusted) with Subject / Issuer / Thumbprint / Valid-window / Actions columns, status banner after each action with success or warning kind ('file missing' = another admin handled it), FleetAdmin-only via [Authorize(Roles=AdminRoles.FleetAdmin)]. Each action invokes LogActionAsync which Serilog-logs the authenticated admin user + thumbprint + action for an audit trail — DB-level ConfigAuditLog persistence is deferred because its schema is cluster-scoped and cert actions are cluster-agnostic; Serilog + CertTrustService's filesystem-op info logs give the forensic trail in the meantime. Sidebar link added to MainLayout between Reservations and the future Account page.
Tests — CertTrustServiceTests (9 new unit cases): ListRejected parses Subject + Thumbprint + store kind from a self-signed test cert written into rejected/certs/; rejected and trusted stores are kept separate; TrustRejected moves the file and the Rejected list is empty afterwards; TrustRejected with a thumbprint not in rejected returns false without touching trusted; DeleteRejected removes the file; UntrustCert removes from trusted only; thumbprint match is case-insensitive (operator UX); missing store directories produce empty lists instead of throwing DirectoryNotFoundException (pristine-install tolerance); a junk .der in the store is logged + skipped and the valid certs still surface (one bad file doesn't break the page). Full Admin.Tests Unit suite: 23 pass / 0 fail (14 prior + 9 new). Full Admin build clean — 0 errors, 0 warnings.
lmx-followups.md #3 marked DONE with a cross-reference to this PR and a note that flipping AutoAcceptUntrustedClientCertificates to false as the production default is a deployment-config follow-up, not a code gap — the Admin UI is now ready to be the trust gate.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/v2/lmx-followups.md

@@ -41,17 +41,22 @@ can't write a `Tune` attribute unless it also carries `WriteTune`.
 See `feedback_acl_at_server_layer.md` in memory for the architectural directive
 that authz stays at the server layer and never delegates to driver-specific auth.
 
-## 3. Admin UI client-cert trust management
+## 3. Admin UI client-cert trust management — **DONE (PR 28)**
 
-**Status**: Server side auto-accepts untrusted client certs when the
-`AutoAcceptUntrustedClientCertificates` option is true (dev default).
-Production deployments want operator-controlled trust via the Admin UI.
+PR 28 shipped `/certificates` in the Admin UI. `CertTrustService` reads the OPC
+UA server's PKI store root (`OpcUaServerOptions.PkiStoreRoot` — default
+`%ProgramData%\OtOpcUa\pki`) and lists rejected + trusted certs by parsing the
+`.der` files directly, so it has no `Opc.Ua` dependency and runs on any
+Admin host that can reach the shared PKI directory.
 
-**To do**:
-- Surface the server's rejected-certificate store in the Admin UI.
-- Page to move certs between `rejected` / `trusted`.
-- Flip `AutoAcceptUntrustedClientCertificates` to false once Admin UI is the
-  trust gate.
+Operator actions: Trust (moves `rejected/certs/*.der` → `trusted/certs/*.der`),
+Delete rejected, Revoke trust. The OPC UA stack re-reads the trusted store on
+each new client handshake, so no explicit reload signal is needed —
+operators retry the rejected client's connection after trusting.
+
+Deferred: flipping `AutoAcceptUntrustedClientCertificates` to `false` as the
+deployment default. That's a production-hardening config change, not a code
+gap — the Admin UI is now ready to be the trust gate.
 
 ## 4. Live-LDAP integration test