Use caddy's certmagic library for extensible/robust ACME handling (#14177)

* use certmagic for more extensible/robust ACME cert handling

* accept TOS based on config option

Signed-off-by: Andrew Thornton <art27@cantab.net>

Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: Lauris BH <lauris@nix.lv>

vendor/github.com/miekg/dns/tlsa.go

@@ -0,0 +1,44 @@
+package dns
+
+import (
+	"crypto/x509"
+	"net"
+	"strconv"
+)
+
+// Sign creates a TLSA record from an SSL certificate.
+func (r *TLSA) Sign(usage, selector, matchingType int, cert *x509.Certificate) (err error) {
+	r.Hdr.Rrtype = TypeTLSA
+	r.Usage = uint8(usage)
+	r.Selector = uint8(selector)
+	r.MatchingType = uint8(matchingType)
+
+	r.Certificate, err = CertificateToDANE(r.Selector, r.MatchingType, cert)
+	return err
+}
+
+// Verify verifies a TLSA record against an SSL certificate. If it is OK
+// a nil error is returned.
+func (r *TLSA) Verify(cert *x509.Certificate) error {
+	c, err := CertificateToDANE(r.Selector, r.MatchingType, cert)
+	if err != nil {
+		return err // Not also ErrSig?
+	}
+	if r.Certificate == c {
+		return nil
+	}
+	return ErrSig // ErrSig, really?
+}
+
+// TLSAName returns the ownername of a TLSA resource record as per the
+// rules specified in RFC 6698, Section 3.
+func TLSAName(name, service, network string) (string, error) {
+	if !IsFqdn(name) {
+		return "", ErrFqdn
+	}
+	p, err := net.LookupPort(network, service)
+	if err != nil {
+		return "", err
+	}
+	return "_" + strconv.Itoa(p) + "._" + network + "." + name, nil
+}