The web UI's certificate from Let's Encrypt, through Jarl

tls.acme names the certificate and jarl: the Jarl server and a token that
may only write the challenge record. Steward gets the certificate with
DNS-01 (lego), writing the record through Jarl's API into every view that
has the zone, renews it with a third of its lifetime left and swaps it
in without a restart. A check runs before every order: Jarl, the zone,
the token's permission, a test record, the zone's name servers, public
resolvers, clean-up; each step says what to fix. Staging by default.

With a certificate, each listener serves HTTPS and plain HTTP on one port
(redirecting plain HTTP, except from the server itself).

steward cert / cert check / cert renew, Server -> Certificate in the web
UI, GET /certificate, POST /certificate/check|renew. docs/certificates.md
and docs/jarl.md (the Jarl user and the token's grant).

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

internal/server/sniff_test.go

@@ -0,0 +1,58 @@
+package server
+
+import (
+	"context"
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"crypto/rand"
+	"crypto/tls"
+	"crypto/x509"
+	"crypto/x509/pkix"
+	"encoding/pem"
+	"io"
+	"math/big"
+	"net"
+	"net/http"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+	"time"
+)
+
+// TestHTTPSAndPlainOnOnePort serves a certificate file: the same port
+// answers HTTPS, and plain HTTP from loopback.
+func TestHTTPSAndPlainOnOnePort(t *testing.T) {
+	dir := t.TempDir()
+	key, _ := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
+	tmpl := &x509.Certificate{SerialNumber: big.NewInt(1), Subject: pkix.Name{CommonName: "dhcp.test"}, DNSNames: []string{"dhcp.test"},
+		NotBefore: time.Now().Add(-time.Hour), NotAfter: time.Now().Add(time.Hour)}
+	der, _ := x509.CreateCertificate(rand.Reader, tmpl, tmpl, &key.PublicKey, key)
+	kd, _ := x509.MarshalPKCS8PrivateKey(key)
+	os.WriteFile(filepath.Join(dir, "c.pem"), pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: der}), 0o600)
+	os.WriteFile(filepath.Join(dir, "k.pem"), pem.EncodeToMemory(&pem.Block{Type: "PRIVATE KEY", Bytes: kd}), 0o600)
+	ln, _ := net.Listen("tcp", "127.0.0.1:0")
+	addr := ln.Addr().String()
+	ln.Close()
+	e := newEnv(t)
+	e.srv.cfg.Listen, e.srv.cfg.TLSCertFile, e.srv.cfg.TLSKeyFile = []string{addr}, filepath.Join(dir, "c.pem"), filepath.Join(dir, "k.pem")
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	ready := make(chan struct{})
+	go e.srv.Serve(ctx, func() { close(ready) })
+	<-ready
+	pool := x509.NewCertPool()
+	pool.AddCert(func() *x509.Certificate { c, _ := x509.ParseCertificate(der); return c }())
+	hc := &http.Client{Timeout: 5 * time.Second, Transport: &http.Transport{TLSClientConfig: &tls.Config{RootCAs: pool, ServerName: "dhcp.test"}}}
+	for _, url := range []string{"https://" + addr + "/healthz", "http://" + addr + "/healthz"} {
+		resp, err := hc.Get(url)
+		if err != nil {
+			t.Fatalf("%s: %v", url, err)
+		}
+		b, _ := io.ReadAll(resp.Body)
+		resp.Body.Close()
+		if resp.StatusCode != 200 || !strings.Contains(string(b), `"ok":true`) {
+			t.Errorf("%s: %d %s", url, resp.StatusCode, b)
+		}
+	}
+}