Harden auth, headers, and container per OWASP review

- Add per-account lockout + IP rate limiter on local sign-in (A07)
- Emit CSP and security headers on every response (A05)
- Run container as non-root `app`, /data 0700 (A05/A02)
- Stop reflecting raw token-endpoint body into redirect URL (A09)
- Handle missing refresh_token in connect callback without a 500

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

SECURITY-TODO.md

@@ -2,6 +2,8 @@
 
 Review date: 2026-06-11. Items 1–4 and 6 fixed the same day; #5 reviewed and accepted by design.
 
+Second pass (OWASP Top 10), 2026-06-11: items 7–11 below found and fixed the same day.
+
 ---
 
 ## 1. [HIGH] ✅ FIXED — Open redirect in `/connect/initiate` leaked SharePoint session tokens
@@ -49,3 +51,43 @@ Review date: 2026-06-11. Items 1–4 and 6 fixed the same day; #5 reviewed and a
 **Was:** `/admin/users` and `/admin/audit` used `@attribute [Authorize]` (any authenticated user) plus an in-markup `if (Role != Admin) return;`.
 
 **Fix:** Added an `Admin` authorization policy (`RequireClaim("app_role", "Admin")`) in [Program.cs](Program.cs) and both pages now use `[Authorize(Policy = "Admin")]` ([UserManagement.razor](Components/Pages/Admin/UserManagement.razor), [AuditLogs.razor](Components/Pages/Admin/AuditLogs.razor)). A claim-value policy (not `[Authorize(Roles=…)]`) was used deliberately: the local/dev sign-in identities don't set a `ClaimTypes.Role` claim, so a Roles check would have silently denied local admins. The in-component checks were kept as defense-in-depth.
+
+---
+
+## 7. [MEDIUM] ✅ FIXED — No brute-force protection on local sign-in (OWASP A07)
+
+**Was:** `/account/local-login` and `UserService.ValidateLocalCredentialsAsync` had no rate limiting and no account lockout, leaving local accounts (incl. the bootstrap admin) open to unlimited password guessing — relevant given the plain-HTTP/LAN bootstrap deployment mode.
+
+**Fix:** Two layers. (1) A per-account lockout on `AppUser` (`FailedLoginCount`/`LockoutEndUtc`) — 5 consecutive failures → 15-minute lock, counter cleared on success ([UserService.cs](Services/Auth/UserService.cs), [AppUser.cs](Core/Models/AppUser.cs)). A locked account is refused before the password is even checked, and failure stays generic (no enumeration). (2) An IP-partitioned fixed-window rate limiter (`"login"` policy, 10/min) on `/account/local-login` and `/account/login/entra` ([Program.cs](Program.cs)). The account lockout is the control that holds up when `X-Forwarded-For` is spoofed/rotated (forwarded headers are trusted from any source — see #3); the IP limiter is the coarse volumetric layer.
+
+---
+
+## 8. [MEDIUM] ✅ FIXED — Missing security response headers (OWASP A05)
+
+**Was:** No `Content-Security-Policy`, `X-Frame-Options`, `X-Content-Type-Options`, or `Referrer-Policy`. A clickjacked page could drive the victim's live Blazor Server circuit, and there was no CSP backstop against injected script.
+
+**Fix:** A middleware emits these on every response ([Program.cs](Program.cs)). CSP is tuned to the app: all scripts are external so `script-src 'self'` (no `unsafe-*`); `style-src` keeps `'unsafe-inline'` for the login page's inline `<style>` and the components' `style=""`; `img-src 'self' data:` for base64 client logos / download links; `connect-src 'self'` for the SignalR WebSocket; `frame-ancestors 'none'` (+ `X-Frame-Options: DENY`) blocks clickjacking.
+
+---
+
+## 9. [LOW-MEDIUM] ✅ FIXED — Container ran as root; `/data` world-readable (OWASP A05 / A02)
+
+**Was:** The [Dockerfile](Dockerfile) had no `USER` directive, so the process ran as root and the `/data` volume (Data Protection keys, app-only certs, user store) had default permissions. The DP keys decrypt the auth cookie, the browser-stored SharePoint refresh tokens, and the on-disk certs — a large blast radius for anyone able to read the volume.
+
+**Fix:** Final image now creates `/data` owned by the shipped non-root `app` user with mode `0700`, then `USER app` ([Dockerfile](Dockerfile)). Docker seeds a fresh named volume from that ownership/mode, so the running user can write it while other host users can't read the keys/certs at rest. (DP keys themselves remain unencrypted at rest — inherent to file-based keys in a container; the volume permissions are the mitigation.)
+
+---
+
+## 10. [LOW] ✅ FIXED — Raw token-endpoint response reflected into the redirect URL (OWASP A09)
+
+**Was:** `/connect/callback` put the raw Azure token-endpoint JSON (and the provider's verbose `error_description`) into `?connect_error=…`, landing in browser history and — behind the proxy — proxy access logs. Those bodies can carry correlation/trace ids and claim hints.
+
+**Fix:** The token-endpoint failure body and the verbose `error_description` are now logged server-side via `ILogger`; the redirect carries only a generic notice (or the short, safe OAuth `error` code) ([OAuthEndpoints.cs](Infrastructure/OAuth/OAuthEndpoints.cs)).
+
+---
+
+## 11. [LOW] ✅ FIXED — `/connect/callback` threw a 500 when no refresh_token was returned
+
+**Was:** `root.GetProperty("refresh_token").GetString()!` threw `KeyNotFoundException` (→ 500 + stack trace in non-prod) when the tenant/app withheld `offline_access`.
+
+**Fix:** Uses `TryGetProperty`; a missing/empty refresh token is logged and redirects with a friendly `connect_error` instead of throwing ([OAuthEndpoints.cs](Infrastructure/OAuth/OAuthEndpoints.cs)).