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>

go.mod

@@ -3,21 +3,29 @@ module steward
 go 1.27.1
 
 require (
+	github.com/go-acme/lego/v4 v4.35.2
+	github.com/miekg/dns v1.1.73
+	github.com/spf13/cobra v1.10.2
+	go.yaml.in/yaml/v3 v3.0.5
+	golang.org/x/crypto v0.57.0
+	golang.org/x/net v0.58.0
+	golang.org/x/term v0.46.0
+	modernc.org/sqlite v1.60.1
+)
+
+require (
+	github.com/cenkalti/backoff/v5 v5.0.3 // indirect
 	github.com/dustin/go-humanize v1.0.1 // indirect
+	github.com/go-jose/go-jose/v4 v4.1.4 // indirect
 	github.com/google/uuid v1.6.0 // indirect
 	github.com/inconshreveable/mousetrap v1.1.0 // indirect
 	github.com/mattn/go-isatty v0.0.24 // indirect
 	github.com/ncruces/go-strftime v1.0.0 // indirect
 	github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec // indirect
-	github.com/spf13/cobra v1.10.2 // indirect
 	github.com/spf13/pflag v1.0.9 // indirect
-	go.yaml.in/yaml/v3 v3.0.5 // indirect
-	golang.org/x/crypto v0.57.0 // indirect
-	golang.org/x/net v0.58.0 // indirect
 	golang.org/x/sys v0.48.0 // indirect
-	golang.org/x/term v0.46.0 // indirect
+	golang.org/x/text v0.42.0 // indirect
 	modernc.org/libc v1.77.1 // indirect
 	modernc.org/mathutil v1.7.1 // indirect
 	modernc.org/memory v1.12.1 // indirect
-	modernc.org/sqlite v1.60.1 // indirect
 )