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/dnssec_keygen.go

@@ -0,0 +1,140 @@
+package dns
+
+import (
+	"crypto"
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"crypto/rand"
+	"crypto/rsa"
+	"math/big"
+
+	"golang.org/x/crypto/ed25519"
+)
+
+// Generate generates a DNSKEY of the given bit size.
+// The public part is put inside the DNSKEY record.
+// The Algorithm in the key must be set as this will define
+// what kind of DNSKEY will be generated.
+// The ECDSA algorithms imply a fixed keysize, in that case
+// bits should be set to the size of the algorithm.
+func (k *DNSKEY) Generate(bits int) (crypto.PrivateKey, error) {
+	switch k.Algorithm {
+	case RSAMD5, DSA, DSANSEC3SHA1:
+		return nil, ErrAlg
+	case RSASHA1, RSASHA256, RSASHA1NSEC3SHA1:
+		if bits < 512 || bits > 4096 {
+			return nil, ErrKeySize
+		}
+	case RSASHA512:
+		if bits < 1024 || bits > 4096 {
+			return nil, ErrKeySize
+		}
+	case ECDSAP256SHA256:
+		if bits != 256 {
+			return nil, ErrKeySize
+		}
+	case ECDSAP384SHA384:
+		if bits != 384 {
+			return nil, ErrKeySize
+		}
+	case ED25519:
+		if bits != 256 {
+			return nil, ErrKeySize
+		}
+	}
+
+	switch k.Algorithm {
+	case RSASHA1, RSASHA256, RSASHA512, RSASHA1NSEC3SHA1:
+		priv, err := rsa.GenerateKey(rand.Reader, bits)
+		if err != nil {
+			return nil, err
+		}
+		k.setPublicKeyRSA(priv.PublicKey.E, priv.PublicKey.N)
+		return priv, nil
+	case ECDSAP256SHA256, ECDSAP384SHA384:
+		var c elliptic.Curve
+		switch k.Algorithm {
+		case ECDSAP256SHA256:
+			c = elliptic.P256()
+		case ECDSAP384SHA384:
+			c = elliptic.P384()
+		}
+		priv, err := ecdsa.GenerateKey(c, rand.Reader)
+		if err != nil {
+			return nil, err
+		}
+		k.setPublicKeyECDSA(priv.PublicKey.X, priv.PublicKey.Y)
+		return priv, nil
+	case ED25519:
+		pub, priv, err := ed25519.GenerateKey(rand.Reader)
+		if err != nil {
+			return nil, err
+		}
+		k.setPublicKeyED25519(pub)
+		return priv, nil
+	default:
+		return nil, ErrAlg
+	}
+}
+
+// Set the public key (the value E and N)
+func (k *DNSKEY) setPublicKeyRSA(_E int, _N *big.Int) bool {
+	if _E == 0 || _N == nil {
+		return false
+	}
+	buf := exponentToBuf(_E)
+	buf = append(buf, _N.Bytes()...)
+	k.PublicKey = toBase64(buf)
+	return true
+}
+
+// Set the public key for Elliptic Curves
+func (k *DNSKEY) setPublicKeyECDSA(_X, _Y *big.Int) bool {
+	if _X == nil || _Y == nil {
+		return false
+	}
+	var intlen int
+	switch k.Algorithm {
+	case ECDSAP256SHA256:
+		intlen = 32
+	case ECDSAP384SHA384:
+		intlen = 48
+	}
+	k.PublicKey = toBase64(curveToBuf(_X, _Y, intlen))
+	return true
+}
+
+// Set the public key for Ed25519
+func (k *DNSKEY) setPublicKeyED25519(_K ed25519.PublicKey) bool {
+	if _K == nil {
+		return false
+	}
+	k.PublicKey = toBase64(_K)
+	return true
+}
+
+// Set the public key (the values E and N) for RSA
+// RFC 3110: Section 2. RSA Public KEY Resource Records
+func exponentToBuf(_E int) []byte {
+	var buf []byte
+	i := big.NewInt(int64(_E)).Bytes()
+	if len(i) < 256 {
+		buf = make([]byte, 1, 1+len(i))
+		buf[0] = uint8(len(i))
+	} else {
+		buf = make([]byte, 3, 3+len(i))
+		buf[0] = 0
+		buf[1] = uint8(len(i) >> 8)
+		buf[2] = uint8(len(i))
+	}
+	buf = append(buf, i...)
+	return buf
+}
+
+// Set the public key for X and Y for Curve. The two
+// values are just concatenated.
+func curveToBuf(_X, _Y *big.Int, intlen int) []byte {
+	buf := intToBytes(_X, intlen)
+	buf = append(buf, intToBytes(_Y, intlen)...)
+	return buf
+}