TLS certificates: Jarl obtains and renews them over ACME

Jarl is now an ACME client (lego's core, no DNS providers). It answers
DNS-01 challenges in a zone it serves, or through Porkbun's DNS API while
Porkbun serves the domain; "auto" decides from the domain's public name
servers at every renewal, and a CNAME on _acme-challenge is followed.
Certificates are used for jarld's HTTPS (served without a restart; each
port speaks HTTPS and plain HTTP, plain HTTP from loopback and trusted
proxies still served) and/or written for named's DNS over TLS/HTTPS, with
rndc reconfig on renewal. Renewal follows the CA's ARI window or two
thirds of the lifetime, with back-off. Certificates you renew yourself
can be used too. Certificates page and dashboard card, jarl cert,
/api/v1/certificates, Prometheus gauges, docs/certificates.md, and an
e2e section against Pebble.

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

internal/certs/inspect.go

@@ -0,0 +1,118 @@
+// Package certs manages TLS certificates (docs/certificates.md): ones Jarl
+// obtains and renews itself over ACME, answering the DNS-01 challenges in
+// its own zones or at Porkbun, and ones you renew yourself that Jarl only
+// reads. A certificate is used for jarld's HTTPS ("web") and/or written
+// where named can read it ("dns", for DNS over TLS and HTTPS).
+package certs
+
+import (
+	"crypto/ecdsa"
+	"crypto/ed25519"
+	"crypto/rsa"
+	"crypto/tls"
+	"crypto/x509"
+	"errors"
+	"fmt"
+	"strings"
+	"time"
+)
+
+// Info is what a certificate says about itself.
+type Info struct {
+	Names     []string
+	NotBefore time.Time
+	NotAfter  time.Time
+	Issuer    string
+	Serial    string
+	KeyType   string // ec256, ec384, rsa2048, ...
+	Leaf      *x509.Certificate
+	// Warnings are problems that don't stop it working everywhere (a
+	// missing intermediate certificate).
+	Warnings []string
+}
+
+// Inspect checks that certPEM (the certificate, then its intermediates)
+// and keyPEM belong together and returns what the certificate says, and
+// the pair ready to serve.
+func Inspect(certPEM, keyPEM []byte) (*Info, *tls.Certificate, error) {
+	pair, err := tls.X509KeyPair(certPEM, keyPEM)
+	if err != nil {
+		msg := err.Error()
+		switch {
+		case strings.Contains(msg, "private key does not match public key"):
+			return nil, nil, errors.New("the key doesn't belong to the certificate")
+		case strings.Contains(msg, "failed to find any PEM data in certificate"):
+			return nil, nil, errors.New("no certificate found (expected PEM: -----BEGIN CERTIFICATE-----)")
+		case strings.Contains(msg, "failed to find any PEM data in key"), strings.Contains(msg, "failed to find PEM block with type ending in \"PRIVATE KEY\""):
+			return nil, nil, errors.New("no private key found (expected PEM: -----BEGIN ... PRIVATE KEY-----)")
+		}
+		return nil, nil, err
+	}
+	leaf := pair.Leaf
+	if leaf == nil {
+		if leaf, err = x509.ParseCertificate(pair.Certificate[0]); err != nil {
+			return nil, nil, err
+		}
+		pair.Leaf = leaf
+	}
+	in := &Info{NotBefore: leaf.NotBefore, NotAfter: leaf.NotAfter, Serial: fmt.Sprintf("%x", leaf.SerialNumber), Leaf: leaf, KeyType: keyType(leaf)}
+	in.Names = append(in.Names, leaf.DNSNames...)
+	for _, ip := range leaf.IPAddresses {
+		in.Names = append(in.Names, ip.String())
+	}
+	if len(in.Names) == 0 && leaf.Subject.CommonName != "" {
+		in.Names = []string{leaf.Subject.CommonName}
+	}
+	in.Issuer = leaf.Issuer.CommonName
+	if len(leaf.Issuer.Organization) > 0 {
+		if in.Issuer == "" {
+			in.Issuer = leaf.Issuer.Organization[0]
+		} else {
+			in.Issuer = leaf.Issuer.Organization[0] + " " + in.Issuer
+		}
+	}
+	selfSigned := leaf.Issuer.String() == leaf.Subject.String()
+	if len(pair.Certificate) == 1 && !selfSigned {
+		in.Warnings = append(in.Warnings, "the file holds only the certificate, without its intermediate certificate: many clients will reject it; use the full chain (fullchain.pem)")
+	}
+	return in, &pair, nil
+}
+
+func keyType(c *x509.Certificate) string {
+	switch k := c.PublicKey.(type) {
+	case *ecdsa.PublicKey:
+		return fmt.Sprintf("ec%d", k.Curve.Params().BitSize)
+	case *rsa.PublicKey:
+		return fmt.Sprintf("rsa%d", k.N.BitLen())
+	case ed25519.PublicKey:
+		return "ed25519"
+	}
+	return "unknown"
+}
+
+// Covers reports whether the certificate names cover every name in want
+// (a wildcard covers one label).
+func Covers(names, want []string) bool {
+	for _, w := range want {
+		if !covered(names, w) {
+			return false
+		}
+	}
+	return true
+}
+
+func covered(names []string, want string) bool {
+	want = strings.ToLower(strings.TrimSuffix(want, "."))
+	for _, n := range names {
+		n = strings.ToLower(n)
+		if n == want {
+			return true
+		}
+		if base, ok := strings.CutPrefix(n, "*."); ok && !strings.HasPrefix(want, "*.") {
+			if _, rest, ok := strings.Cut(want, "."); ok && rest == base {
+				return true
+			}
+		}
+	}
+	return false
+}