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/server.go

@@ -19,6 +19,7 @@ import (
 	"time"
 
 	"steward/internal/auth"
+	"steward/internal/certs"
 	"steward/internal/dhcpd"
 	"steward/internal/engine"
 	"steward/internal/store"
@@ -40,6 +41,9 @@ type Config struct {
 	Socket string
 	// PingProblem says why the ping check can't run (nil: always fine).
 	PingProblem func() string
+	// ACME keeps the certificate stewardd obtains itself (tls.acme; nil
+	// when off).
+	ACME *certs.Manager
 }
 
 // Interfaces lists the host's interfaces.
@@ -106,6 +110,9 @@ func (s *Server) Serve(ctx context.Context, ready func()) error {
 	if len(s.cfg.Listen) == 0 {
 		return errors.New("no listen addresses configured")
 	}
+	// With a certificate (tls.cert_file, or one stewardd obtains, which
+	// may turn up later), each listener serves HTTPS and plain HTTP side
+	// by side (sniff.go); plain HTTP is redirected once there is one.
 	var tlsCfg *tls.Config
 	if s.cfg.TLSCertFile != "" {
 		cr, err := newCertReloader(s.cfg.TLSCertFile, s.cfg.TLSKeyFile, s.log)
@@ -113,7 +120,9 @@ func (s *Server) Serve(ctx context.Context, ready func()) error {
 			return err
 		}
 		s.certs = cr
-		tlsCfg = &tls.Config{MinVersion: tls.VersionTLS12, GetCertificate: cr.get, NextProtos: []string{"h2", "http/1.1"}}
+	}
+	if s.certs != nil || s.cfg.ACME != nil {
+		tlsCfg = &tls.Config{MinVersion: tls.VersionTLS12, GetCertificate: s.webCertificate, NextProtos: []string{"h2", "http/1.1"}}
 	}
 	errc := make(chan error, len(s.cfg.Listen)+1)
 	var listeners []net.Listener
@@ -131,8 +140,12 @@ func (s *Server) Serve(ctx context.Context, ready func()) error {
 		listeners = append(listeners, ln)
 	}
 	for i, ln := range listeners {
+		handler := s.Handler()
+		if tlsCfg != nil {
+			handler = s.requireHTTPS(handler)
+		}
 		srv := &http.Server{
-			Handler:           s.Handler(),
+			Handler:           handler,
 			ReadHeaderTimeout: 10 * time.Second,
 			ReadTimeout:       2 * time.Minute,
 			WriteTimeout:      5 * time.Minute,
@@ -145,11 +158,16 @@ func (s *Server) Serve(ctx context.Context, ready func()) error {
 		s.mu.Unlock()
 		scheme := "http"
 		if tlsCfg != nil {
-			scheme = "https"
-			ln = tls.NewListener(ln, tlsCfg)
-		} else if host, _, err := net.SplitHostPort(s.cfg.Listen[i]); err == nil {
-			if ip, err := netip.ParseAddr(host); host == "" || err == nil && !ip.IsLoopback() {
-				s.log.Warn("serving plain HTTP on a non-loopback address: passwords and API tokens travel unencrypted; configure tls or a TLS reverse proxy", "addr", s.cfg.Listen[i])
+			if s.httpsAvailable() {
+				scheme = "https"
+			}
+			ln = newSniffListener(ln, tlsCfg)
+		}
+		if !s.httpsAvailable() && s.cfg.ACME == nil {
+			if host, _, err := net.SplitHostPort(s.cfg.Listen[i]); err == nil {
+				if ip, err := netip.ParseAddr(host); host == "" || err == nil && !ip.IsLoopback() {
+					s.log.Warn("serving plain HTTP on a non-loopback address: passwords and API tokens travel unencrypted; configure tls or a TLS reverse proxy", "addr", s.cfg.Listen[i])
+				}
 			}
 		}
 		s.log.Info("listening", "addr", s.cfg.Listen[i], "url", scheme+"://"+ln.Addr().String())