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9b1a210 Dec 16, 2016
@x1ddos @titanous @bradfitz
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// Copyright 2016 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package autocert provides automatic access to certificates from Let's Encrypt
// and any other ACME-based CA.
//
// This package is a work in progress and makes no API stability promises.
package autocert
import (
"bytes"
"crypto"
"crypto/ecdsa"
"crypto/elliptic"
"crypto/rand"
"crypto/rsa"
"crypto/tls"
"crypto/x509"
"crypto/x509/pkix"
"encoding/pem"
"errors"
"fmt"
"io"
mathrand "math/rand"
"net/http"
"strconv"
"strings"
"sync"
"time"
"golang.org/x/crypto/acme"
"golang.org/x/net/context"
)
// pseudoRand is safe for concurrent use.
var pseudoRand *lockedMathRand
func init() {
src := mathrand.NewSource(timeNow().UnixNano())
pseudoRand = &lockedMathRand{rnd: mathrand.New(src)}
}
// AcceptTOS always returns true to indicate the acceptance of a CA Terms of Service
// during account registration.
func AcceptTOS(tosURL string) bool { return true }
// HostPolicy specifies which host names the Manager is allowed to respond to.
// It returns a non-nil error if the host should be rejected.
// The returned error is accessible via tls.Conn.Handshake and its callers.
// See Manager's HostPolicy field and GetCertificate method docs for more details.
type HostPolicy func(ctx context.Context, host string) error
// HostWhitelist returns a policy where only the specified host names are allowed.
// Only exact matches are currently supported. Subdomains, regexp or wildcard
// will not match.
func HostWhitelist(hosts ...string) HostPolicy {
whitelist := make(map[string]bool, len(hosts))
for _, h := range hosts {
whitelist[h] = true
}
return func(_ context.Context, host string) error {
if !whitelist[host] {
return errors.New("acme/autocert: host not configured")
}
return nil
}
}
// defaultHostPolicy is used when Manager.HostPolicy is not set.
func defaultHostPolicy(context.Context, string) error {
return nil
}
// Manager is a stateful certificate manager built on top of acme.Client.
// It obtains and refreshes certificates automatically,
// as well as providing them to a TLS server via tls.Config.
//
// A simple usage example:
//
// m := autocert.Manager{
// Prompt: autocert.AcceptTOS,
// HostPolicy: autocert.HostWhitelist("example.org"),
// }
// s := &http.Server{
// Addr: ":https",
// TLSConfig: &tls.Config{GetCertificate: m.GetCertificate},
// }
// s.ListenAndServeTLS("", "")
//
// To preserve issued certificates and improve overall performance,
// use a cache implementation of Cache. For instance, DirCache.
type Manager struct {
// Prompt specifies a callback function to conditionally accept a CA's Terms of Service (TOS).
// The registration may require the caller to agree to the CA's TOS.
// If so, Manager calls Prompt with a TOS URL provided by the CA. Prompt should report
// whether the caller agrees to the terms.
//
// To always accept the terms, the callers can use AcceptTOS.
Prompt func(tosURL string) bool
// Cache optionally stores and retrieves previously-obtained certificates.
// If nil, certs will only be cached for the lifetime of the Manager.
//
// Manager passes the Cache certificates data encoded in PEM, with private/public
// parts combined in a single Cache.Put call, private key first.
Cache Cache
// HostPolicy controls which domains the Manager will attempt
// to retrieve new certificates for. It does not affect cached certs.
//
// If non-nil, HostPolicy is called before requesting a new cert.
// If nil, all hosts are currently allowed. This is not recommended,
// as it opens a potential attack where clients connect to a server
// by IP address and pretend to be asking for an incorrect host name.
// Manager will attempt to obtain a certificate for that host, incorrectly,
// eventually reaching the CA's rate limit for certificate requests
// and making it impossible to obtain actual certificates.
//
// See GetCertificate for more details.
HostPolicy HostPolicy
// RenewBefore optionally specifies how early certificates should
// be renewed before they expire.
//
// If zero, they're renewed 1 week before expiration.
RenewBefore time.Duration
// Client is used to perform low-level operations, such as account registration
// and requesting new certificates.
// If Client is nil, a zero-value acme.Client is used with acme.LetsEncryptURL
// directory endpoint and a newly-generated ECDSA P-256 key.
//
// Mutating the field after the first call of GetCertificate method will have no effect.
Client *acme.Client
// Email optionally specifies a contact email address.
// This is used by CAs, such as Let's Encrypt, to notify about problems
// with issued certificates.
//
// If the Client's account key is already registered, Email is not used.
Email string
// ForceRSA makes the Manager generate certificates with 2048-bit RSA keys.
//
// If false, a default is used. Currently the default
// is EC-based keys using the P-256 curve.
ForceRSA bool
clientMu sync.Mutex
client *acme.Client // initialized by acmeClient method
stateMu sync.Mutex
state map[string]*certState // keyed by domain name
// tokenCert is keyed by token domain name, which matches server name
// of ClientHello. Keys always have ".acme.invalid" suffix.
tokenCertMu sync.RWMutex
tokenCert map[string]*tls.Certificate
// renewal tracks the set of domains currently running renewal timers.
// It is keyed by domain name.
renewalMu sync.Mutex
renewal map[string]*domainRenewal
}
// GetCertificate implements the tls.Config.GetCertificate hook.
// It provides a TLS certificate for hello.ServerName host, including answering
// *.acme.invalid (TLS-SNI) challenges. All other fields of hello are ignored.
//
// If m.HostPolicy is non-nil, GetCertificate calls the policy before requesting
// a new cert. A non-nil error returned from m.HostPolicy halts TLS negotiation.
// The error is propagated back to the caller of GetCertificate and is user-visible.
// This does not affect cached certs. See HostPolicy field description for more details.
func (m *Manager) GetCertificate(hello *tls.ClientHelloInfo) (*tls.Certificate, error) {
name := hello.ServerName
if name == "" {
return nil, errors.New("acme/autocert: missing server name")
}
// check whether this is a token cert requested for TLS-SNI challenge
if strings.HasSuffix(name, ".acme.invalid") {
m.tokenCertMu.RLock()
defer m.tokenCertMu.RUnlock()
if cert := m.tokenCert[name]; cert != nil {
return cert, nil
}
if cert, err := m.cacheGet(name); err == nil {
return cert, nil
}
// TODO: cache error results?
return nil, fmt.Errorf("acme/autocert: no token cert for %q", name)
}
// regular domain
name = strings.TrimSuffix(name, ".") // golang.org/issue/18114
cert, err := m.cert(name)
if err == nil {
return cert, nil
}
if err != ErrCacheMiss {
return nil, err
}
// first-time
ctx := context.Background() // TODO: use a deadline?
if err := m.hostPolicy()(ctx, name); err != nil {
return nil, err
}
cert, err = m.createCert(ctx, name)
if err != nil {
return nil, err
}
m.cachePut(name, cert)
return cert, nil
}
// cert returns an existing certificate either from m.state or cache.
// If a certificate is found in cache but not in m.state, the latter will be filled
// with the cached value.
func (m *Manager) cert(name string) (*tls.Certificate, error) {
m.stateMu.Lock()
if s, ok := m.state[name]; ok {
m.stateMu.Unlock()
s.RLock()
defer s.RUnlock()
return s.tlscert()
}
defer m.stateMu.Unlock()
cert, err := m.cacheGet(name)
if err != nil {
return nil, err
}
signer, ok := cert.PrivateKey.(crypto.Signer)
if !ok {
return nil, errors.New("acme/autocert: private key cannot sign")
}
if m.state == nil {
m.state = make(map[string]*certState)
}
s := &certState{
key: signer,
cert: cert.Certificate,
leaf: cert.Leaf,
}
m.state[name] = s
go m.renew(name, s.key, s.leaf.NotAfter)
return cert, nil
}
// cacheGet always returns a valid certificate, or an error otherwise.
func (m *Manager) cacheGet(domain string) (*tls.Certificate, error) {
if m.Cache == nil {
return nil, ErrCacheMiss
}
// TODO: might want to define a cache timeout on m
ctx := context.Background()
data, err := m.Cache.Get(ctx, domain)
if err != nil {
return nil, err
}
// private
priv, pub := pem.Decode(data)
if priv == nil || !strings.Contains(priv.Type, "PRIVATE") {
return nil, errors.New("acme/autocert: no private key found in cache")
}
privKey, err := parsePrivateKey(priv.Bytes)
if err != nil {
return nil, err
}
// public
var pubDER [][]byte
for len(pub) > 0 {
var b *pem.Block
b, pub = pem.Decode(pub)
if b == nil {
break
}
pubDER = append(pubDER, b.Bytes)
}
if len(pub) > 0 {
return nil, errors.New("acme/autocert: invalid public key")
}
// verify and create TLS cert
leaf, err := validCert(domain, pubDER, privKey)
if err != nil {
return nil, err
}
tlscert := &tls.Certificate{
Certificate: pubDER,
PrivateKey: privKey,
Leaf: leaf,
}
return tlscert, nil
}
func (m *Manager) cachePut(domain string, tlscert *tls.Certificate) error {
if m.Cache == nil {
return nil
}
// contains PEM-encoded data
var buf bytes.Buffer
// private
switch key := tlscert.PrivateKey.(type) {
case *ecdsa.PrivateKey:
if err := encodeECDSAKey(&buf, key); err != nil {
return err
}
case *rsa.PrivateKey:
b := x509.MarshalPKCS1PrivateKey(key)
pb := &pem.Block{Type: "RSA PRIVATE KEY", Bytes: b}
if err := pem.Encode(&buf, pb); err != nil {
return err
}
default:
return errors.New("acme/autocert: unknown private key type")
}
// public
for _, b := range tlscert.Certificate {
pb := &pem.Block{Type: "CERTIFICATE", Bytes: b}
if err := pem.Encode(&buf, pb); err != nil {
return err
}
}
// TODO: might want to define a cache timeout on m
ctx := context.Background()
return m.Cache.Put(ctx, domain, buf.Bytes())
}
func encodeECDSAKey(w io.Writer, key *ecdsa.PrivateKey) error {
b, err := x509.MarshalECPrivateKey(key)
if err != nil {
return err
}
pb := &pem.Block{Type: "EC PRIVATE KEY", Bytes: b}
return pem.Encode(w, pb)
}
// createCert starts the domain ownership verification and returns a certificate
// for that domain upon success.
//
// If the domain is already being verified, it waits for the existing verification to complete.
// Either way, createCert blocks for the duration of the whole process.
func (m *Manager) createCert(ctx context.Context, domain string) (*tls.Certificate, error) {
// TODO: maybe rewrite this whole piece using sync.Once
state, err := m.certState(domain)
if err != nil {
return nil, err
}
// state may exist if another goroutine is already working on it
// in which case just wait for it to finish
if !state.locked {
state.RLock()
defer state.RUnlock()
return state.tlscert()
}
// We are the first; state is locked.
// Unblock the readers when domain ownership is verified
// and the we got the cert or the process failed.
defer state.Unlock()
state.locked = false
der, leaf, err := m.authorizedCert(ctx, state.key, domain)
if err != nil {
return nil, err
}
state.cert = der
state.leaf = leaf
go m.renew(domain, state.key, state.leaf.NotAfter)
return state.tlscert()
}
// certState returns a new or existing certState.
// If a new certState is returned, state.exist is false and the state is locked.
// The returned error is non-nil only in the case where a new state could not be created.
func (m *Manager) certState(domain string) (*certState, error) {
m.stateMu.Lock()
defer m.stateMu.Unlock()
if m.state == nil {
m.state = make(map[string]*certState)
}
// existing state
if state, ok := m.state[domain]; ok {
return state, nil
}
// new locked state
var (
err error
key crypto.Signer
)
if m.ForceRSA {
key, err = rsa.GenerateKey(rand.Reader, 2048)
} else {
key, err = ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
}
if err != nil {
return nil, err
}
state := &certState{
key: key,
locked: true,
}
state.Lock() // will be unlocked by m.certState caller
m.state[domain] = state
return state, nil
}
// authorizedCert starts domain ownership verification process and requests a new cert upon success.
// The key argument is the certificate private key.
func (m *Manager) authorizedCert(ctx context.Context, key crypto.Signer, domain string) (der [][]byte, leaf *x509.Certificate, err error) {
// TODO: make m.verify retry or retry m.verify calls here
if err := m.verify(ctx, domain); err != nil {
return nil, nil, err
}
client, err := m.acmeClient(ctx)
if err != nil {
return nil, nil, err
}
csr, err := certRequest(key, domain)
if err != nil {
return nil, nil, err
}
der, _, err = client.CreateCert(ctx, csr, 0, true)
if err != nil {
return nil, nil, err
}
leaf, err = validCert(domain, der, key)
if err != nil {
return nil, nil, err
}
return der, leaf, nil
}
// verify starts a new identifier (domain) authorization flow.
// It prepares a challenge response and then blocks until the authorization
// is marked as "completed" by the CA (either succeeded or failed).
//
// verify returns nil iff the verification was successful.
func (m *Manager) verify(ctx context.Context, domain string) error {
client, err := m.acmeClient(ctx)
if err != nil {
return err
}
// start domain authorization and get the challenge
authz, err := client.Authorize(ctx, domain)
if err != nil {
return err
}
// maybe don't need to at all
if authz.Status == acme.StatusValid {
return nil
}
// pick a challenge: prefer tls-sni-02 over tls-sni-01
// TODO: consider authz.Combinations
var chal *acme.Challenge
for _, c := range authz.Challenges {
if c.Type == "tls-sni-02" {
chal = c
break
}
if c.Type == "tls-sni-01" {
chal = c
}
}
if chal == nil {
return errors.New("acme/autocert: no supported challenge type found")
}
// create a token cert for the challenge response
var (
cert tls.Certificate
name string
)
switch chal.Type {
case "tls-sni-01":
cert, name, err = client.TLSSNI01ChallengeCert(chal.Token)
case "tls-sni-02":
cert, name, err = client.TLSSNI02ChallengeCert(chal.Token)
default:
err = fmt.Errorf("acme/autocert: unknown challenge type %q", chal.Type)
}
if err != nil {
return err
}
m.putTokenCert(name, &cert)
defer func() {
// verification has ended at this point
// don't need token cert anymore
go m.deleteTokenCert(name)
}()
// ready to fulfill the challenge
if _, err := client.Accept(ctx, chal); err != nil {
return err
}
// wait for the CA to validate
_, err = client.WaitAuthorization(ctx, authz.URI)
return err
}
// putTokenCert stores the cert under the named key in both m.tokenCert map
// and m.Cache.
func (m *Manager) putTokenCert(name string, cert *tls.Certificate) {
m.tokenCertMu.Lock()
defer m.tokenCertMu.Unlock()
if m.tokenCert == nil {
m.tokenCert = make(map[string]*tls.Certificate)
}
m.tokenCert[name] = cert
m.cachePut(name, cert)
}
// deleteTokenCert removes the token certificate for the specified domain name
// from both m.tokenCert map and m.Cache.
func (m *Manager) deleteTokenCert(name string) {
m.tokenCertMu.Lock()
defer m.tokenCertMu.Unlock()
delete(m.tokenCert, name)
if m.Cache != nil {
m.Cache.Delete(context.Background(), name)
}
}
// renew starts a cert renewal timer loop, one per domain.
//
// The loop is scheduled in two cases:
// - a cert was fetched from cache for the first time (wasn't in m.state)
// - a new cert was created by m.createCert
//
// The key argument is a certificate private key.
// The exp argument is the cert expiration time (NotAfter).
func (m *Manager) renew(domain string, key crypto.Signer, exp time.Time) {
m.renewalMu.Lock()
defer m.renewalMu.Unlock()
if m.renewal[domain] != nil {
// another goroutine is already on it
return
}
if m.renewal == nil {
m.renewal = make(map[string]*domainRenewal)
}
dr := &domainRenewal{m: m, domain: domain, key: key}
m.renewal[domain] = dr
dr.start(exp)
}
// stopRenew stops all currently running cert renewal timers.
// The timers are not restarted during the lifetime of the Manager.
func (m *Manager) stopRenew() {
m.renewalMu.Lock()
defer m.renewalMu.Unlock()
for name, dr := range m.renewal {
delete(m.renewal, name)
dr.stop()
}
}
func (m *Manager) accountKey(ctx context.Context) (crypto.Signer, error) {
const keyName = "acme_account.key"
genKey := func() (*ecdsa.PrivateKey, error) {
return ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
}
if m.Cache == nil {
return genKey()
}
data, err := m.Cache.Get(ctx, keyName)
if err == ErrCacheMiss {
key, err := genKey()
if err != nil {
return nil, err
}
var buf bytes.Buffer
if err := encodeECDSAKey(&buf, key); err != nil {
return nil, err
}
if err := m.Cache.Put(ctx, keyName, buf.Bytes()); err != nil {
return nil, err
}
return key, nil
}
if err != nil {
return nil, err
}
priv, _ := pem.Decode(data)
if priv == nil || !strings.Contains(priv.Type, "PRIVATE") {
return nil, errors.New("acme/autocert: invalid account key found in cache")
}
return parsePrivateKey(priv.Bytes)
}
func (m *Manager) acmeClient(ctx context.Context) (*acme.Client, error) {
m.clientMu.Lock()
defer m.clientMu.Unlock()
if m.client != nil {
return m.client, nil
}
client := m.Client
if client == nil {
client = &acme.Client{DirectoryURL: acme.LetsEncryptURL}
}
if client.Key == nil {
var err error
client.Key, err = m.accountKey(ctx)
if err != nil {
return nil, err
}
}
var contact []string
if m.Email != "" {
contact = []string{"mailto:" + m.Email}
}
a := &acme.Account{Contact: contact}
_, err := client.Register(ctx, a, m.Prompt)
if ae, ok := err.(*acme.Error); err == nil || ok && ae.StatusCode == http.StatusConflict {
// conflict indicates the key is already registered
m.client = client
err = nil
}
return m.client, err
}
func (m *Manager) hostPolicy() HostPolicy {
if m.HostPolicy != nil {
return m.HostPolicy
}
return defaultHostPolicy
}
func (m *Manager) renewBefore() time.Duration {
if m.RenewBefore > maxRandRenew {
return m.RenewBefore
}
return 7 * 24 * time.Hour // 1 week
}
// certState is ready when its mutex is unlocked for reading.
type certState struct {
sync.RWMutex
locked bool // locked for read/write
key crypto.Signer // private key for cert
cert [][]byte // DER encoding
leaf *x509.Certificate // parsed cert[0]; always non-nil if cert != nil
}
// tlscert creates a tls.Certificate from s.key and s.cert.
// Callers should wrap it in s.RLock() and s.RUnlock().
func (s *certState) tlscert() (*tls.Certificate, error) {
if s.key == nil {
return nil, errors.New("acme/autocert: missing signer")
}
if len(s.cert) == 0 {
return nil, errors.New("acme/autocert: missing certificate")
}
return &tls.Certificate{
PrivateKey: s.key,
Certificate: s.cert,
Leaf: s.leaf,
}, nil
}
// certRequest creates a certificate request for the given common name cn
// and optional SANs.
func certRequest(key crypto.Signer, cn string, san ...string) ([]byte, error) {
req := &x509.CertificateRequest{
Subject: pkix.Name{CommonName: cn},
DNSNames: san,
}
return x509.CreateCertificateRequest(rand.Reader, req, key)
}
// Attempt to parse the given private key DER block. OpenSSL 0.9.8 generates
// PKCS#1 private keys by default, while OpenSSL 1.0.0 generates PKCS#8 keys.
// OpenSSL ecparam generates SEC1 EC private keys for ECDSA. We try all three.
//
// Inspired by parsePrivateKey in crypto/tls/tls.go.
func parsePrivateKey(der []byte) (crypto.Signer, error) {
if key, err := x509.ParsePKCS1PrivateKey(der); err == nil {
return key, nil
}
if key, err := x509.ParsePKCS8PrivateKey(der); err == nil {
switch key := key.(type) {
case *rsa.PrivateKey:
return key, nil
case *ecdsa.PrivateKey:
return key, nil
default:
return nil, errors.New("acme/autocert: unknown private key type in PKCS#8 wrapping")
}
}
if key, err := x509.ParseECPrivateKey(der); err == nil {
return key, nil
}
return nil, errors.New("acme/autocert: failed to parse private key")
}
// validCert parses a cert chain provided as der argument and verifies the leaf, der[0],
// corresponds to the private key, as well as the domain match and expiration dates.
// It doesn't do any revocation checking.
//
// The returned value is the verified leaf cert.
func validCert(domain string, der [][]byte, key crypto.Signer) (leaf *x509.Certificate, err error) {
// parse public part(s)
var n int
for _, b := range der {
n += len(b)
}
pub := make([]byte, n)
n = 0
for _, b := range der {
n += copy(pub[n:], b)
}
x509Cert, err := x509.ParseCertificates(pub)
if len(x509Cert) == 0 {
return nil, errors.New("acme/autocert: no public key found")
}
// verify the leaf is not expired and matches the domain name
leaf = x509Cert[0]
now := timeNow()
if now.Before(leaf.NotBefore) {
return nil, errors.New("acme/autocert: certificate is not valid yet")
}
if now.After(leaf.NotAfter) {
return nil, errors.New("acme/autocert: expired certificate")
}
if err := leaf.VerifyHostname(domain); err != nil {
return nil, err
}
// ensure the leaf corresponds to the private key
switch pub := leaf.PublicKey.(type) {
case *rsa.PublicKey:
prv, ok := key.(*rsa.PrivateKey)
if !ok {
return nil, errors.New("acme/autocert: private key type does not match public key type")
}
if pub.N.Cmp(prv.N) != 0 {
return nil, errors.New("acme/autocert: private key does not match public key")
}
case *ecdsa.PublicKey:
prv, ok := key.(*ecdsa.PrivateKey)
if !ok {
return nil, errors.New("acme/autocert: private key type does not match public key type")
}
if pub.X.Cmp(prv.X) != 0 || pub.Y.Cmp(prv.Y) != 0 {
return nil, errors.New("acme/autocert: private key does not match public key")
}
default:
return nil, errors.New("acme/autocert: unknown public key algorithm")
}
return leaf, nil
}
func retryAfter(v string) time.Duration {
if i, err := strconv.Atoi(v); err == nil {
return time.Duration(i) * time.Second
}
if t, err := http.ParseTime(v); err == nil {
return t.Sub(timeNow())
}
return time.Second
}
type lockedMathRand struct {
sync.Mutex
rnd *mathrand.Rand
}
func (r *lockedMathRand) int63n(max int64) int64 {
r.Lock()
n := r.rnd.Int63n(max)
r.Unlock()
return n
}
// for easier testing
var timeNow = time.Now