Split the console from the resolver: fancy-dns-console writes the cluster

fancy-dns-console is a second binary holding the web UI, authentication and
every edit. It writes ClientGroup, BlockList and DNSZone objects through the new
kubeedit package and forwards all other /api routes to a running resolver
with its own key, dropping the browser's credentials, so it can run in the
cluster or on a workstation with a kubeconfig and nothing about the resolver's
placement matters. The resolver never imports kubeedit and the console is not on
the DNS path.

kubeedit validates every spec with the runtime's own converters
(kubesource.CheckGroup/CheckList/CheckZone) before writing, so the console
cannot store an object the resolver would reject. Zone edits keep the
file-based writer's behaviour: duplicate and below-a-delegation records are
refused, a delegation in a new zone also gives the zone its servers, and a
zone with no apex NS is never stored. Each object records the editing user in
an annotation; updates retry on conflict.

The resolver reports groups from ClientGroup objects as source "kubernetes" and
counter-only rows (the "(default)" bucket, or a group removed since) as
"history", and lists DNSZone zones as the editable ones. The console uses that
to leave the YAML's groups alone and to drop history rows, which the UI would
otherwise send back on save. Its GET /api/clients overlays the cluster's
current objects on the resolver's list, because the resolver only sees an edit
after its watch fires and a save made just after another would delete the
first.

An end-to-end test runs both halves against one fake apiserver: a group saved
through the console refuses queries, a zone built record by record answers
authoritatively, and a request with the resolver's own key is rejected by the
console.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

internal/console/console.go

@@ -0,0 +1,120 @@
+// Package console is the editing and viewing half of fancy-dns, split from the
+// resolver so that it can run somewhere else. It owns authentication and the
+// web UI, writes ClientGroup, BlockList and DNSZone objects to the cluster, and
+// forwards everything the resolver owns (statistics, the query log, the cache)
+// to the resolver's admin API.
+//
+// The resolver never calls the console and the console is never on the DNS
+// path: stopping it cannot affect a query.
+package console
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"log/slog"
+	"net/http"
+	"strings"
+	"time"
+
+	"git.k8s-git-k6n.net/mats/fancy-dns/internal/api"
+	"git.k8s-git-k6n.net/mats/fancy-dns/internal/config"
+	"git.k8s-git-k6n.net/mats/fancy-dns/internal/kubeedit"
+	"git.k8s-git-k6n.net/mats/fancy-dns/internal/web"
+)
+
+// Options configure a Console.
+type Options struct {
+	Config  *config.Store
+	Runtime *Runtime
+	Editor  *kubeedit.Editor
+	Logger  *slog.Logger
+	Version string
+}
+
+// Console serves the UI and the edit API.
+type Console struct {
+	opt     Options
+	log     *slog.Logger
+	api     *api.Server
+	started time.Time
+}
+
+// New builds a Console.
+func New(opt Options) (*Console, error) {
+	if opt.Config == nil || opt.Runtime == nil || opt.Editor == nil {
+		return nil, errors.New("console: config, runtime and editor are required")
+	}
+	if opt.Logger == nil {
+		opt.Logger = slog.Default()
+	}
+	c := &Console{opt: opt, log: opt.Logger.With("component", "console"), started: time.Now()}
+	srv, err := api.New(c.hooks())
+	if err != nil {
+		return nil, err
+	}
+	c.api = srv
+	return c, nil
+}
+
+// actor names who is making a request, for the object annotation.
+func actor(ctx context.Context) string {
+	if p, ok := api.PrincipalFrom(ctx); ok && p.Name != "" {
+		return p.Name
+	}
+	return ""
+}
+
+// Handler is the whole HTTP surface: the console's own routes, the resolver's
+// API behind the same authentication, and the single-page app.
+func (c *Console) Handler() (http.Handler, error) {
+	cfg := c.opt.Config.Get()
+	base := strings.TrimSuffix(cfg.API.BasePath, "/")
+	own := c.api.Handler()
+
+	mux := http.NewServeMux()
+	// Handled by the shared API server: authentication, the identity of the
+	// caller, and the edits whose hooks write to the cluster.
+	for _, p := range []string{
+		base + "/auth/",
+		"GET " + base + "/whoami",
+		"GET " + base + "/healthz",
+		"PUT " + base + "/clients",
+		"POST " + base + "/zones/records",
+		"PUT " + base + "/zones/records",
+		"DELETE " + base + "/zones/records",
+		"POST " + base + "/zones/delegations",
+		"DELETE " + base + "/zones/delegations",
+		"DELETE " + base + "/zones",
+		"POST " + base + "/blocklists/toggle",
+	} {
+		mux.Handle(p, own)
+	}
+
+	// Reads that combine the cluster's objects with the resolver's view.
+	mux.Handle("GET "+base+"/zones", c.api.Protect(http.HandlerFunc(c.handleZones), false))
+	mux.Handle("GET "+base+"/clients", c.api.Protect(http.HandlerFunc(c.handleClients), false))
+	mux.Handle("GET "+base+"/blocklist-sources", c.api.Protect(http.HandlerFunc(c.handleListSources), false))
+	mux.Handle("PUT "+base+"/blocklist-sources/{name}", c.api.Protect(http.HandlerFunc(c.handleListSourcePut), true))
+	mux.Handle("DELETE "+base+"/blocklist-sources/{name}", c.api.Protect(http.HandlerFunc(c.handleListSourceDelete), true))
+
+	// Everything else under the API belongs to the resolver.
+	proxy := c.opt.Runtime.Proxy()
+	read, write := c.api.Protect(proxy, false), c.api.Protect(proxy, true)
+	mux.Handle(base+"/", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.Method == http.MethodGet || r.Method == http.MethodHead {
+			read.ServeHTTP(w, r)
+			return
+		}
+		write.ServeHTTP(w, r)
+	}))
+
+	if cfg.API.UI {
+		ui, err := web.Handler("")
+		if err != nil {
+			return nil, fmt.Errorf("web console: %w", err)
+		}
+		mux.Handle("/", ui)
+	}
+	return mux, nil
+}