Give every view a TSIG key that selects it

Each view's match-clients starts with "key jarl-view-NAME" (after
"!key" for the views listed after it), so a query signed with a view's
key lands in that view from any address. The secrets are derived from a
random seed in Jarl's database. The delegation check signs its queries
to this server's own addresses with the key of the zone's view: before,
they got whichever view matched the server's address, usually internal.
jarl view key / GET /views/{id}/key show a key for dig -k (tsig:write,
audited). jarl-view- key names are reserved; the importer drops view
keys from a configuration Jarl wrote.

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

internal/nscheck/localkey_test.go

@@ -0,0 +1,52 @@
+package nscheck
+
+import (
+	"context"
+	"net"
+	"net/netip"
+	"testing"
+	"time"
+
+	"github.com/miekg/dns"
+)
+
+// A query to this host's own address is signed with LocalKey, so a server
+// with views answers from the view that key selects.
+func TestLocalKey(t *testing.T) {
+	zone := "example.com."
+	key := &Key{Name: "jarl-view-external.", Algorithm: "hmac-sha256", Secret: "c2VjcmV0LXNlY3JldC1zZWNyZXQtc2VjcmV0LXNlY3I="}
+	pc, err := net.ListenPacket("udp", "127.0.0.1:0")
+	if err != nil {
+		t.Skip(err)
+	}
+	_, port, _ := net.SplitHostPort(pc.LocalAddr().String())
+	srv := &dns.Server{PacketConn: pc, TsigSecret: map[string]string{key.Name: key.Secret},
+		Handler: dns.HandlerFunc(func(w dns.ResponseWriter, req *dns.Msg) {
+			// Signed with the view key: the "external" view's serial.
+			serial := "1"
+			signed := req.IsTsig() != nil && w.TsigStatus() == nil
+			if signed {
+				serial = "2"
+			}
+			m := new(dns.Msg)
+			m.SetReply(req)
+			m.Authoritative = true
+			m.Answer = []dns.RR{rr(zone + " 3600 IN SOA ns1." + zone + " admin." + zone + " " + serial + " 3600 900 1209600 300")}
+			if signed {
+				m.SetTsig(key.Name, dns.HmacSHA256, 300, time.Now().Unix())
+			}
+			w.WriteMsg(m)
+		})}
+	go srv.ActivateAndServe()
+	t.Cleanup(func() { srv.Shutdown() })
+
+	ref := uint32(2)
+	c := &Checker{Timeout: time.Second, Port: port, IsLocal: func(netip.Addr) bool { return false }}
+	if res := c.Serials(context.Background(), zone, &ref, []Target{{Addresses: []string{"127.0.0.1"}}}); res[0].Status != "behind" {
+		t.Errorf("unsigned: %+v (want the other view's serial)", res[0])
+	}
+	c.LocalKey = key
+	if res := c.Serials(context.Background(), zone, &ref, []Target{{Addresses: []string{"127.0.0.1"}}}); res[0].Status != "in_sync" {
+		t.Errorf("signed with the view key: %+v", res[0])
+	}
+}