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/mholt/acmez/acme/jws.go

@@ -0,0 +1,263 @@
+// Copyright 2020 Matthew Holt
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// --- ORIGINAL LICENSE ---
+//
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the THIRD-PARTY file.
+//
+// (This file has been modified from its original contents.)
+// (And it has dragons. Don't wake the dragons.)
+
+package acme
+
+import (
+	"crypto"
+	"crypto/ecdsa"
+	"crypto/hmac"
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/sha256"
+	_ "crypto/sha512" // need for EC keys
+	"encoding/base64"
+	"encoding/json"
+	"fmt"
+	"math/big"
+)
+
+var errUnsupportedKey = fmt.Errorf("unknown key type; only RSA and ECDSA are supported")
+
+// keyID is the account identity provided by a CA during registration.
+type keyID string
+
+// noKeyID indicates that jwsEncodeJSON should compute and use JWK instead of a KID.
+// See jwsEncodeJSON for details.
+const noKeyID = keyID("")
+
+// // noPayload indicates jwsEncodeJSON will encode zero-length octet string
+// // in a JWS request. This is called POST-as-GET in RFC 8555 and is used to make
+// // authenticated GET requests via POSTing with an empty payload.
+// // See https://tools.ietf.org/html/rfc8555#section-6.3 for more details.
+// const noPayload = ""
+
+// jwsEncodeEAB creates a JWS payload for External Account Binding according to RFC 8555 §7.3.4.
+func jwsEncodeEAB(accountKey crypto.PublicKey, hmacKey []byte, kid keyID, url string) ([]byte, error) {
+	// §7.3.4: "The 'alg' field MUST indicate a MAC-based algorithm"
+	alg, sha := "HS256", crypto.SHA256
+
+	// §7.3.4: "The 'nonce' field MUST NOT be present"
+	phead, err := jwsHead(alg, "", url, kid, nil)
+	if err != nil {
+		return nil, err
+	}
+
+	encodedKey, err := jwkEncode(accountKey)
+	if err != nil {
+		return nil, err
+	}
+	payload := base64.RawURLEncoding.EncodeToString([]byte(encodedKey))
+
+	payloadToSign := []byte(phead + "." + payload)
+
+	h := hmac.New(sha256.New, hmacKey)
+	h.Write(payloadToSign)
+	sig := h.Sum(nil)
+
+	return jwsFinal(sha, sig, phead, payload)
+}
+
+// jwsEncodeJSON signs claimset using provided key and a nonce.
+// The result is serialized in JSON format containing either kid or jwk
+// fields based on the provided keyID value.
+//
+// If kid is non-empty, its quoted value is inserted in the protected head
+// as "kid" field value. Otherwise, JWK is computed using jwkEncode and inserted
+// as "jwk" field value. The "jwk" and "kid" fields are mutually exclusive.
+//
+// See https://tools.ietf.org/html/rfc7515#section-7.
+//
+// If nonce is empty, it will not be encoded into the header.
+func jwsEncodeJSON(claimset interface{}, key crypto.Signer, kid keyID, nonce, url string) ([]byte, error) {
+	alg, sha := jwsHasher(key.Public())
+	if alg == "" || !sha.Available() {
+		return nil, errUnsupportedKey
+	}
+
+	phead, err := jwsHead(alg, nonce, url, kid, key)
+	if err != nil {
+		return nil, err
+	}
+
+	var payload string
+	if claimset != nil {
+		cs, err := json.Marshal(claimset)
+		if err != nil {
+			return nil, err
+		}
+		payload = base64.RawURLEncoding.EncodeToString(cs)
+	}
+
+	payloadToSign := []byte(phead + "." + payload)
+	hash := sha.New()
+	_, _ = hash.Write(payloadToSign)
+	digest := hash.Sum(nil)
+
+	sig, err := jwsSign(key, sha, digest)
+	if err != nil {
+		return nil, err
+	}
+
+	return jwsFinal(sha, sig, phead, payload)
+}
+
+// jwkEncode encodes public part of an RSA or ECDSA key into a JWK.
+// The result is also suitable for creating a JWK thumbprint.
+// https://tools.ietf.org/html/rfc7517
+func jwkEncode(pub crypto.PublicKey) (string, error) {
+	switch pub := pub.(type) {
+	case *rsa.PublicKey:
+		// https://tools.ietf.org/html/rfc7518#section-6.3.1
+		n := pub.N
+		e := big.NewInt(int64(pub.E))
+		// Field order is important.
+		// See https://tools.ietf.org/html/rfc7638#section-3.3 for details.
+		return fmt.Sprintf(`{"e":"%s","kty":"RSA","n":"%s"}`,
+			base64.RawURLEncoding.EncodeToString(e.Bytes()),
+			base64.RawURLEncoding.EncodeToString(n.Bytes()),
+		), nil
+	case *ecdsa.PublicKey:
+		// https://tools.ietf.org/html/rfc7518#section-6.2.1
+		p := pub.Curve.Params()
+		n := p.BitSize / 8
+		if p.BitSize%8 != 0 {
+			n++
+		}
+		x := pub.X.Bytes()
+		if n > len(x) {
+			x = append(make([]byte, n-len(x)), x...)
+		}
+		y := pub.Y.Bytes()
+		if n > len(y) {
+			y = append(make([]byte, n-len(y)), y...)
+		}
+		// Field order is important.
+		// See https://tools.ietf.org/html/rfc7638#section-3.3 for details.
+		return fmt.Sprintf(`{"crv":"%s","kty":"EC","x":"%s","y":"%s"}`,
+			p.Name,
+			base64.RawURLEncoding.EncodeToString(x),
+			base64.RawURLEncoding.EncodeToString(y),
+		), nil
+	}
+	return "", errUnsupportedKey
+}
+
+// jwsHead constructs the protected JWS header for the given fields.
+// Since jwk and kid are mutually-exclusive, the jwk will be encoded
+// only if kid is empty. If nonce is empty, it will not be encoded.
+func jwsHead(alg, nonce, url string, kid keyID, key crypto.Signer) (string, error) {
+	phead := fmt.Sprintf(`{"alg":%q`, alg)
+	if kid == noKeyID {
+		jwk, err := jwkEncode(key.Public())
+		if err != nil {
+			return "", err
+		}
+		phead += fmt.Sprintf(`,"jwk":%s`, jwk)
+	} else {
+		phead += fmt.Sprintf(`,"kid":%q`, kid)
+	}
+	if nonce != "" {
+		phead += fmt.Sprintf(`,"nonce":%q`, nonce)
+	}
+	phead += fmt.Sprintf(`,"url":%q}`, url)
+	phead = base64.RawURLEncoding.EncodeToString([]byte(phead))
+	return phead, nil
+}
+
+// jwsFinal constructs the final JWS object.
+func jwsFinal(sha crypto.Hash, sig []byte, phead, payload string) ([]byte, error) {
+	enc := struct {
+		Protected string `json:"protected"`
+		Payload   string `json:"payload"`
+		Sig       string `json:"signature"`
+	}{
+		Protected: phead,
+		Payload:   payload,
+		Sig:       base64.RawURLEncoding.EncodeToString(sig),
+	}
+	result, err := json.Marshal(&enc)
+	if err != nil {
+		return nil, err
+	}
+	return result, nil
+}
+
+// jwsSign signs the digest using the given key.
+// The hash is unused for ECDSA keys.
+//
+// Note: non-stdlib crypto.Signer implementations are expected to return
+// the signature in the format as specified in RFC7518.
+// See https://tools.ietf.org/html/rfc7518 for more details.
+func jwsSign(key crypto.Signer, hash crypto.Hash, digest []byte) ([]byte, error) {
+	if key, ok := key.(*ecdsa.PrivateKey); ok {
+		// The key.Sign method of ecdsa returns ASN1-encoded signature.
+		// So, we use the package Sign function instead
+		// to get R and S values directly and format the result accordingly.
+		r, s, err := ecdsa.Sign(rand.Reader, key, digest)
+		if err != nil {
+			return nil, err
+		}
+		rb, sb := r.Bytes(), s.Bytes()
+		size := key.Params().BitSize / 8
+		if size%8 > 0 {
+			size++
+		}
+		sig := make([]byte, size*2)
+		copy(sig[size-len(rb):], rb)
+		copy(sig[size*2-len(sb):], sb)
+		return sig, nil
+	}
+	return key.Sign(rand.Reader, digest, hash)
+}
+
+// jwsHasher indicates suitable JWS algorithm name and a hash function
+// to use for signing a digest with the provided key.
+// It returns ("", 0) if the key is not supported.
+func jwsHasher(pub crypto.PublicKey) (string, crypto.Hash) {
+	switch pub := pub.(type) {
+	case *rsa.PublicKey:
+		return "RS256", crypto.SHA256
+	case *ecdsa.PublicKey:
+		switch pub.Params().Name {
+		case "P-256":
+			return "ES256", crypto.SHA256
+		case "P-384":
+			return "ES384", crypto.SHA384
+		case "P-521":
+			return "ES512", crypto.SHA512
+		}
+	}
+	return "", 0
+}
+
+// jwkThumbprint creates a JWK thumbprint out of pub
+// as specified in https://tools.ietf.org/html/rfc7638.
+func jwkThumbprint(pub crypto.PublicKey) (string, error) {
+	jwk, err := jwkEncode(pub)
+	if err != nil {
+		return "", err
+	}
+	b := sha256.Sum256([]byte(jwk))
+	return base64.RawURLEncoding.EncodeToString(b[:]), nil
+}