// 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 LICENSE file.
// Package acme provides an implementation of the
// Automatic Certificate Management Environment (ACME) spec.
// The intial implementation was based on ACME draft-02 and
// is now being extended to comply with RFC 8555.
// See https://tools.ietf.org/html/draft-ietf-acme-acme-02
// and https://tools.ietf.org/html/rfc8555 for details.
//
// Most common scenarios will want to use autocert subdirectory instead,
// which 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 acme
import (
"context"
"crypto"
"crypto/ecdsa"
"crypto/elliptic"
"crypto/rand"
"crypto/sha256"
"crypto/tls"
"crypto/x509"
"crypto/x509/pkix"
"encoding/asn1"
"encoding/base64"
"encoding/hex"
"encoding/json"
"encoding/pem"
"errors"
"fmt"
"io"
"io/ioutil"
"math/big"
"net/http"
"strings"
"sync"
"time"
)
const (
// LetsEncryptURL is the Directory endpoint of Let's Encrypt CA.
LetsEncryptURL = "https://acme-v02.api.letsencrypt.org/directory"
// ALPNProto is the ALPN protocol name used by a CA server when validating
// tls-alpn-01 challenges.
//
// Package users must ensure their servers can negotiate the ACME ALPN in
// order for tls-alpn-01 challenge verifications to succeed.
// See the crypto/tls package's Config.NextProtos field.
ALPNProto = "acme-tls/1"
)
// idPeACMEIdentifier is the OID for the ACME extension for the TLS-ALPN challenge.
// https://tools.ietf.org/html/draft-ietf-acme-tls-alpn-05#section-5.1
var idPeACMEIdentifier = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 1, 31}
const (
maxChainLen = 5 // max depth and breadth of a certificate chain
maxCertSize = 1 << 20 // max size of a certificate, in DER bytes
// Used for decoding certs from application/pem-certificate-chain response,
// the default when in RFC mode.
maxCertChainSize = maxCertSize * maxChainLen
// Max number of collected nonces kept in memory.
// Expect usual peak of 1 or 2.
maxNonces = 100
)
// Client is an ACME client.
// The only required field is Key. An example of creating a client with a new key
// is as follows:
//
// key, err := rsa.GenerateKey(rand.Reader, 2048)
// if err != nil {
// log.Fatal(err)
// }
// client := &Client{Key: key}
//
type Client struct {
// Key is the account key used to register with a CA and sign requests.
// Key.Public() must return a *rsa.PublicKey or *ecdsa.PublicKey.
//
// The following algorithms are supported:
// RS256, ES256, ES384 and ES512.
// See RFC7518 for more details about the algorithms.
Key crypto.Signer
// HTTPClient optionally specifies an HTTP client to use
// instead of http.DefaultClient.
HTTPClient *http.Client
// DirectoryURL points to the CA directory endpoint.
// If empty, LetsEncryptURL is used.
// Mutating this value after a successful call of Client's Discover method
// will have no effect.
DirectoryURL string
// RetryBackoff computes the duration after which the nth retry of a failed request
// should occur. The value of n for the first call on failure is 1.
// The values of r and resp are the request and response of the last failed attempt.
// If the returned value is negative or zero, no more retries are done and an error
// is returned to the caller of the original method.
//
// Requests which result in a 4xx client error are not retried,
// except for 400 Bad Request due to "bad nonce" errors and 429 Too Many Requests.
//
// If RetryBackoff is nil, a truncated exponential backoff algorithm
// with the ceiling of 10 seconds is used, where each subsequent retry n
// is done after either ("Retry-After" + jitter) or (2^n seconds + jitter),
// preferring the former if "Retry-After" header is found in the resp.
// The jitter is a random value up to 1 second.
RetryBackoff func(n int, r *http.Request, resp *http.Response) time.Duration
// UserAgent is prepended to the User-Agent header sent to the ACME server,
// which by default is this package's name and version.
//
// Reusable libraries and tools in particular should set this value to be
// identifiable by the server, in case they are causing issues.
UserAgent string
cacheMu sync.Mutex
dir *Directory // cached result of Client's Discover method
kid keyID // cached Account.URI obtained from registerRFC or getAccountRFC
noncesMu sync.Mutex
nonces map[string]struct{} // nonces collected from previous responses
}
// accountKID returns a key ID associated with c.Key, the account identity
// provided by the CA during RFC based registration.
// It assumes c.Discover has already been called.
//
// accountKID requires at most one network roundtrip.
// It caches only successful result.
//
// When in pre-RFC mode or when c.getRegRFC responds with an error, accountKID
// returns noKeyID.
func (c *Client) accountKID(ctx context.Context) keyID {
c.cacheMu.Lock()
defer c.cacheMu.Unlock()
if !c.dir.rfcCompliant() {
return noKeyID
}
if c.kid != noKeyID {
return c.kid
}
a, err := c.getRegRFC(ctx)
if err != nil {
return noKeyID
}
c.kid = keyID(a.URI)
return c.kid
}
// Discover performs ACME server discovery using c.DirectoryURL.
//
// It caches successful result. So, subsequent calls will not result in
// a network round-trip. This also means mutating c.DirectoryURL after successful call
// of this method will have no effect.
func (c *Client) Discover(ctx context.Context) (Directory, error) {
c.cacheMu.Lock()
defer c.cacheMu.Unlock()
if c.dir != nil {
return *c.dir, nil
}
res, err := c.get(ctx, c.directoryURL(), wantStatus(http.StatusOK))
if err != nil {
return Directory{}, err
}
defer res.Body.Close()
c.addNonce(res.Header)
var v struct {
Reg string `json:"new-reg"`
RegRFC string `json:"newAccount"`
Authz string `json:"new-authz"`
AuthzRFC string `json:"newAuthz"`
OrderRFC string `json:"newOrder"`
Cert string `json:"new-cert"`
Revoke string `json:"revoke-cert"`
RevokeRFC string `json:"revokeCert"`
NonceRFC string `json:"newNonce"`
KeyChangeRFC string `json:"keyChange"`
Meta struct {
Terms string `json:"terms-of-service"`
TermsRFC string `json:"termsOfService"`
WebsiteRFC string `json:"website"`
CAA []string `json:"caa-identities"`
CAARFC []string `json:"caaIdentities"`
ExternalAcctRFC bool `json:"externalAccountRequired"`
}
}
if err := json.NewDecoder(res.Body).Decode(&v); err != nil {
return Directory{}, err
}
if v.OrderRFC == "" {
// Non-RFC compliant ACME CA.
c.dir = &Directory{
RegURL: v.Reg,
AuthzURL: v.Authz,
CertURL: v.Cert,
RevokeURL: v.Revoke,
Terms: v.Meta.Terms,
Website: v.Meta.WebsiteRFC,
CAA: v.Meta.CAA,
}
return *c.dir, nil
}
// RFC compliant ACME CA.
c.dir = &Directory{
RegURL: v.RegRFC,
AuthzURL: v.AuthzRFC,
OrderURL: v.OrderRFC,
RevokeURL: v.RevokeRFC,
NonceURL: v.NonceRFC,
KeyChangeURL: v.KeyChangeRFC,
Terms: v.Meta.TermsRFC,
Website: v.Meta.WebsiteRFC,
CAA: v.Meta.CAARFC,
ExternalAccountRequired: v.Meta.ExternalAcctRFC,
}
return *c.dir, nil
}
func (c *Client) directoryURL() string {
if c.DirectoryURL != "" {
return c.DirectoryURL
}
return LetsEncryptURL
}
// CreateCert requests a new certificate using the Certificate Signing Request csr encoded in DER format.
// It is incompatible with RFC 8555. Callers should use CreateOrderCert when interfacing
// with an RFC-compliant CA.
//
// The exp argument indicates the desired certificate validity duration. CA may issue a certificate
// with a different duration.
// If the bundle argument is true, the returned value will also contain the CA (issuer) certificate chain.
//
// In the case where CA server does not provide the issued certificate in the response,
// CreateCert will poll certURL using c.FetchCert, which will result in additional round-trips.
// In such a scenario, the caller can cancel the polling with ctx.
//
// CreateCert returns an error if the CA's response or chain was unreasonably large.
// Callers are encouraged to parse the returned value to ensure the certificate is valid and has the expected features.
func (c *Client) CreateCert(ctx context.Context, csr []byte, exp time.Duration, bundle bool) (der [][]byte, certURL string, err error) {
if _, err := c.Discover(ctx); err != nil {
return nil, "", err
}
req := struct {
Resource string `json:"resource"`
CSR string `json:"csr"`
NotBefore string `json:"notBefore,omitempty"`
NotAfter string `json:"notAfter,omitempty"`
}{
Resource: "new-cert",
CSR: base64.RawURLEncoding.EncodeToString(csr),
}
now := timeNow()
req.NotBefore = now.Format(time.RFC3339)
if exp > 0 {
req.NotAfter = now.Add(exp).Format(time.RFC3339)
}
res, err := c.post(ctx, nil, c.dir.CertURL, req, wantStatus(http.StatusCreated))
if err != nil {
return nil, "", err
}
defer res.Body.Close()
curl := res.Header.Get("Location") // cert permanent URL
if res.ContentLength == 0 {
// no cert in the body; poll until we get it
cert, err := c.FetchCert(ctx, curl, bundle)
return cert, curl, err
}
// slurp issued cert and CA chain, if requested
cert, err := c.responseCert(ctx, res, bundle)
return cert, curl, err
}
// FetchCert retrieves already issued certificate from the given url, in DER format.
// It retries the request until the certificate is successfully retrieved,
// context is cancelled by the caller or an error response is received.
//
// If the bundle argument is true, the returned value also contains the CA (issuer)
// certificate chain.
//
// FetchCert returns an error if the CA's response or chain was unreasonably large.
// Callers are encouraged to parse the returned value to ensure the certificate is valid
// and has expected features.
func (c *Client) FetchCert(ctx context.Context, url string, bundle bool) ([][]byte, error) {
dir, err := c.Discover(ctx)
if err != nil {
return nil, err
}
if dir.rfcCompliant() {
return c.fetchCertRFC(ctx, url, bundle)
}
// Legacy non-authenticated GET request.
res, err := c.get(ctx, url, wantStatus(http.StatusOK))
if err != nil {
return nil, err
}
return c.responseCert(ctx, res, bundle)
}
// RevokeCert revokes a previously issued certificate cert, provided in DER format.
//
// The key argument, used to sign the request, must be authorized
// to revoke the certificate. It's up to the CA to decide which keys are authorized.
// For instance, the key pair of the certificate may be authorized.
// If the key is nil, c.Key is used instead.
func (c *Client) RevokeCert(ctx context.Context, key crypto.Signer, cert []byte, reason CRLReasonCode) error {
dir, err := c.Discover(ctx)
if err != nil {
return err
}
if dir.rfcCompliant() {
return c.revokeCertRFC(ctx, key, cert, reason)
}
// Legacy CA.
body := &struct {
Resource string `json:"resource"`
Cert string `json:"certificate"`
Reason int `json:"reason"`
}{
Resource: "revoke-cert",
Cert: base64.RawURLEncoding.EncodeToString(cert),
Reason: int(reason),
}
res, err := c.post(ctx, key, dir.RevokeURL, body, wantStatus(http.StatusOK))
if err != nil {
return err
}
defer res.Body.Close()
return nil
}
// AcceptTOS always returns true to indicate the acceptance of a CA's Terms of Service
// during account registration. See Register method of Client for more details.
func AcceptTOS(tosURL string) bool { return true }
// Register creates a new account with the CA using c.Key.
// It returns the registered account. The account acct is not modified.
//
// The registration may require the caller to agree to the CA's Terms of Service (TOS).
// If so, and the account has not indicated the acceptance of the terms (see Account for details),
// Register 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 caller can use AcceptTOS.
//
// When interfacing with an RFC-compliant CA, non-RFC 8555 fields of acct are ignored
// and prompt is called if Directory's Terms field is non-zero.
// Also see Error's Instance field for when a CA requires already registered accounts to agree
// to an updated Terms of Service.
func (c *Client) Register(ctx context.Context, acct *Account, prompt func(tosURL string) bool) (*Account, error) {
dir, err := c.Discover(ctx)
if err != nil {
return nil, err
}
if dir.rfcCompliant() {
return c.registerRFC(ctx, acct, prompt)
}
// Legacy ACME draft registration flow.
a, err := c.doReg(ctx, dir.RegURL, "new-reg", acct)
if err != nil {
return nil, err
}
var accept bool
if a.CurrentTerms != "" && a.CurrentTerms != a.AgreedTerms {
accept = prompt(a.CurrentTerms)
}
if accept {
a.AgreedTerms = a.CurrentTerms
a, err = c.UpdateReg(ctx, a)
}
return a, err
}
// GetReg retrieves an existing account associated with c.Key.
//
// The url argument is an Account URI used with pre-RFC 8555 CAs.
// It is ignored when interfacing with an RFC-compliant CA.
func (c *Client) GetReg(ctx context.Context, url string) (*Account, error) {
dir, err := c.Discover(ctx)
if err != nil {
return nil, err
}
if dir.rfcCompliant() {
return c.getRegRFC(ctx)
}
// Legacy CA.
a, err := c.doReg(ctx, url, "reg", nil)
if err != nil {
return nil, err
}
a.URI = url
return a, nil
}
// UpdateReg updates an existing registration.
// It returns an updated account copy. The provided account is not modified.
//
// When interfacing with RFC-compliant CAs, a.URI is ignored and the account URL
// associated with c.Key is used instead.
func (c *Client) UpdateReg(ctx context.Context, acct *Account) (*Account, error) {
dir, err := c.Discover(ctx)
if err != nil {
return nil, err
}
if dir.rfcCompliant() {
return c.updateRegRFC(ctx, acct)
}
// Legacy CA.
uri := acct.URI
a, err := c.doReg(ctx, uri, "reg", acct)
if err != nil {
return nil, err
}
a.URI = uri
return a, nil
}
// Authorize performs the initial step in the pre-authorization flow,
// as opposed to order-based flow.
// The caller will then need to choose from and perform a set of returned
// challenges using c.Accept in order to successfully complete authorization.
//
// Once complete, the caller can use AuthorizeOrder which the CA
// should provision with the already satisfied authorization.
// For pre-RFC CAs, the caller can proceed directly to requesting a certificate
// using CreateCert method.
//
// If an authorization has been previously granted, the CA may return
// a valid authorization which has its Status field set to StatusValid.
//
// More about pre-authorization can be found at
// https://tools.ietf.org/html/rfc8555#section-7.4.1.
func (c *Client) Authorize(ctx context.Context, domain string) (*Authorization, error) {
return c.authorize(ctx, "dns", domain)
}
// AuthorizeIP is the same as Authorize but requests IP address authorization.
// Clients which successfully obtain such authorization may request to issue
// a certificate for IP addresses.
//
// See the ACME spec extension for more details about IP address identifiers:
// https://tools.ietf.org/html/draft-ietf-acme-ip.
func (c *Client) AuthorizeIP(ctx context.Context, ipaddr string) (*Authorization, error) {
return c.authorize(ctx, "ip", ipaddr)
}
func (c *Client) authorize(ctx context.Context, typ, val string) (*Authorization, error) {
if _, err := c.Discover(ctx); err != nil {
return nil, err
}
type authzID struct {
Type string `json:"type"`
Value string `json:"value"`
}
req := struct {
Resource string `json:"resource"`
Identifier authzID `json:"identifier"`
}{
Resource: "new-authz",
Identifier: authzID{Type: typ, Value: val},
}
res, err := c.post(ctx, nil, c.dir.AuthzURL, req, wantStatus(http.StatusCreated))
if err != nil {
return nil, err
}
defer res.Body.Close()
var v wireAuthz
if err := json.NewDecoder(res.Body).Decode(&v); err != nil {
return nil, fmt.Errorf("acme: invalid response: %v", err)
}
if v.Status != StatusPending && v.Status != StatusValid {
return nil, fmt.Errorf("acme: unexpected status: %s", v.Status)
}
return v.authorization(res.Header.Get("Location")), nil
}
// GetAuthorization retrieves an authorization identified by the given URL.
//
// If a caller needs to poll an authorization until its status is final,
// see the WaitAuthorization method.
func (c *Client) GetAuthorization(ctx context.Context, url string) (*Authorization, error) {
dir, err := c.Discover(ctx)
if err != nil {
return nil, err
}
var res *http.Response
if dir.rfcCompliant() {
res, err = c.postAsGet(ctx, url, wantStatus(http.StatusOK))
} else {
res, err = c.get(ctx, url, wantStatus(http.StatusOK, http.StatusAccepted))
}
if err != nil {
return nil, err
}
defer res.Body.Close()
var v wireAuthz
if err := json.NewDecoder(res.Body).Decode(&v); err != nil {
return nil, fmt.Errorf("acme: invalid response: %v", err)
}
return v.authorization(url), nil
}
// RevokeAuthorization relinquishes an existing authorization identified
// by the given URL.
// The url argument is an Authorization.URI value.
//
// If successful, the caller will be required to obtain a new authorization
// using the Authorize or AuthorizeOrder methods before being able to request
// a new certificate for the domain associated with the authorization.
//
// It does not revoke existing certificates.
func (c *Client) RevokeAuthorization(ctx context.Context, url string) error {
// Required for c.accountKID() when in RFC mode.
if _, err := c.Discover(ctx); err != nil {
return err
}
req := struct {
Resource string `json:"resource"`
Status string `json:"status"`
Delete bool `json:"delete"`
}{
Resource: "authz",
Status: "deactivated",
Delete: true,
}
res, err := c.post(ctx, nil, url, req, wantStatus(http.StatusOK))
if err != nil {
return err
}
defer res.Body.Close()
return nil
}
// WaitAuthorization polls an authorization at the given URL
// until it is in one of the final states, StatusValid or StatusInvalid,
// the ACME CA responded with a 4xx error code, or the context is done.
//
// It returns a non-nil Authorization only if its Status is StatusValid.
// In all other cases WaitAuthorization returns an error.
// If the Status is StatusInvalid, the returned error is of type *AuthorizationError.
func (c *Client) WaitAuthorization(ctx context.Context, url string) (*Authorization, error) {
// Required for c.accountKID() when in RFC mode.
dir, err := c.Discover(ctx)
if err != nil {
return nil, err
}
getfn := c.postAsGet
if !dir.rfcCompliant() {
getfn = c.get
}
for {
res, err := getfn(ctx, url, wantStatus(http.StatusOK, http.StatusAccepted))
if err != nil {
return nil, err
}
var raw wireAuthz
err = json.NewDecoder(res.Body).Decode(&raw)
res.Body.Close()
switch {
case err != nil:
// Skip and retry.
case raw.Status == StatusValid:
return raw.authorization(url), nil
case raw.Status == StatusInvalid:
return nil, raw.error(url)
}
// Exponential backoff is implemented in c.get above.
// This is just to prevent continuously hitting the CA
// while waiting for a final authorization status.
d := retryAfter(res.Header.Get("Retry-After"))
if d == 0 {
// Given that the fastest challenges TLS-SNI and HTTP-01
// require a CA to make at least 1 network round trip
// and most likely persist a challenge state,
// this default delay seems reasonable.
d = time.Second
}
t := time.NewTimer(d)
select {
case <-ctx.Done():
t.Stop()
return nil, ctx.Err()
case <-t.C:
// Retry.
}
}
}
// GetChallenge retrieves the current status of an challenge.
//
// A client typically polls a challenge status using this method.
func (c *Client) GetChallenge(ctx context.Context, url string) (*Challenge, error) {
// Required for c.accountKID() when in RFC mode.
dir, err := c.Discover(ctx)
if err != nil {
return nil, err
}
getfn := c.postAsGet
if !dir.rfcCompliant() {
getfn = c.get
}
res, err := getfn(ctx, url, wantStatus(http.StatusOK, http.StatusAccepted))
if err != nil {
return nil, err
}
defer res.Body.Close()
v := wireChallenge{URI: url}
if err := json.NewDecoder(res.Body).Decode(&v); err != nil {
return nil, fmt.Errorf("acme: invalid response: %v", err)
}
return v.challenge(), nil
}
// Accept informs the server that the client accepts one of its challenges
// previously obtained with c.Authorize.
//
// The server will then perform the validation asynchronously.
func (c *Client) Accept(ctx context.Context, chal *Challenge) (*Challenge, error) {
// Required for c.accountKID() when in RFC mode.
dir, err := c.Discover(ctx)
if err != nil {
return nil, err
}
var req interface{} = json.RawMessage("{}") // RFC-compliant CA
if !dir.rfcCompliant() {
auth, err := keyAuth(c.Key.Public(), chal.Token)
if err != nil {
return nil, err
}
req = struct {
Resource string `json:"resource"`
Type string `json:"type"`
Auth string `json:"keyAuthorization"`
}{
Resource: "challenge",
Type: chal.Type,
Auth: auth,
}
}
res, err := c.post(ctx, nil, chal.URI, req, wantStatus(
http.StatusOK, // according to the spec
http.StatusAccepted, // Let's Encrypt: see https://goo.gl/WsJ7VT (acme-divergences.md)
))
if err != nil {
return nil, err
}
defer res.Body.Close()
var v wireChallenge
if err := json.NewDecoder(res.Body).Decode(&v); err != nil {
return nil, fmt.Errorf("acme: invalid response: %v", err)
}
return v.challenge(), nil
}
// DNS01ChallengeRecord returns a DNS record value for a dns-01 challenge response.
// A TXT record containing the returned value must be provisioned under
// "_acme-challenge" name of the domain being validated.
//
// The token argument is a Challenge.Token value.
func (c *Client) DNS01ChallengeRecord(token string) (string, error) {
ka, err := keyAuth(c.Key.Public(), token)
if err != nil {
return "", err
}
b := sha256.Sum256([]byte(ka))
return base64.RawURLEncoding.EncodeToString(b[:]), nil
}
// HTTP01ChallengeResponse returns the response for an http-01 challenge.
// Servers should respond with the value to HTTP requests at the URL path
// provided by HTTP01ChallengePath to validate the challenge and prove control
// over a domain name.
//
// The token argument is a Challenge.Token value.
func (c *Client) HTTP01ChallengeResponse(token string) (string, error) {
return keyAuth(c.Key.Public(), token)
}
// HTTP01ChallengePath returns the URL path at which the response for an http-01 challenge
// should be provided by the servers.
// The response value can be obtained with HTTP01ChallengeResponse.
//
// The token argument is a Challenge.Token value.
func (c *Client) HTTP01ChallengePath(token string) string {
return "/.well-known/acme-challenge/" + token
}
// TLSSNI01ChallengeCert creates a certificate for TLS-SNI-01 challenge response.
//
// Deprecated: This challenge type is unused in both draft-02 and RFC versions of ACME spec.
func (c *Client) TLSSNI01ChallengeCert(token string, opt ...CertOption) (cert tls.Certificate, name string, err error) {
ka, err := keyAuth(c.Key.Public(), token)
if err != nil {
return tls.Certificate{}, "", err
}
b := sha256.Sum256([]byte(ka))
h := hex.EncodeToString(b[:])
name = fmt.Sprintf("%s.%s.acme.invalid", h[:32], h[32:])
cert, err = tlsChallengeCert([]string{name}, opt)
if err != nil {
return tls.Certificate{}, "", err
}
return cert, name, nil
}
// TLSSNI02ChallengeCert creates a certificate for TLS-SNI-02 challenge response.
//
// Deprecated: This challenge type is unused in both draft-02 and RFC versions of ACME spec.
func (c *Client) TLSSNI02ChallengeCert(token string, opt ...CertOption) (cert tls.Certificate, name string, err error) {
b := sha256.Sum256([]byte(token))
h := hex.EncodeToString(b[:])
sanA := fmt.Sprintf("%s.%s.token.acme.invalid", h[:32], h[32:])
ka, err := keyAuth(c.Key.Public(), token)
if err != nil {
return tls.Certificate{}, "", err
}
b = sha256.Sum256([]byte(ka))
h = hex.EncodeToString(b[:])
sanB := fmt.Sprintf("%s.%s.ka.acme.invalid", h[:32], h[32:])
cert, err = tlsChallengeCert([]string{sanA, sanB}, opt)
if err != nil {
return tls.Certificate{}, "", err
}
return cert, sanA, nil
}
// TLSALPN01ChallengeCert creates a certificate for TLS-ALPN-01 challenge response.
// Servers can present the certificate to validate the challenge and prove control
// over a domain name. For more details on TLS-ALPN-01 see
// https://tools.ietf.org/html/draft-shoemaker-acme-tls-alpn-00#section-3
//
// The token argument is a Challenge.Token value.
// If a WithKey option is provided, its private part signs the returned cert,
// and the public part is used to specify the signee.
// If no WithKey option is provided, a new ECDSA key is generated using P-256 curve.
//
// The returned certificate is valid for the next 24 hours and must be presented only when
// the server name in the TLS ClientHello matches the domain, and the special acme-tls/1 ALPN protocol
// has been specified.
func (c *Client) TLSALPN01ChallengeCert(token, domain string, opt ...CertOption) (cert tls.Certificate, err error) {
ka, err := keyAuth(c.Key.Public(), token)
if err != nil {
return tls.Certificate{}, err
}
shasum := sha256.Sum256([]byte(ka))
extValue, err := asn1.Marshal(shasum[:])
if err != nil {
return tls.Certificate{}, err
}
acmeExtension := pkix.Extension{
Id: idPeACMEIdentifier,
Critical: true,
Value: extValue,
}
tmpl := defaultTLSChallengeCertTemplate()
var newOpt []CertOption
for _, o := range opt {
switch o := o.(type) {
case *certOptTemplate:
t := *(*x509.Certificate)(o) // shallow copy is ok
tmpl = &t
default:
newOpt = append(newOpt, o)
}
}
tmpl.ExtraExtensions = append(tmpl.ExtraExtensions, acmeExtension)
newOpt = append(newOpt, WithTemplate(tmpl))
return tlsChallengeCert([]string{domain}, newOpt)
}
// doReg sends all types of registration requests the old way (pre-RFC world).
// The type of request is identified by typ argument, which is a "resource"
// in the ACME spec terms.
//
// A non-nil acct argument indicates whether the intention is to mutate data
// of the Account. Only Contact and Agreement of its fields are used
// in such cases.
func (c *Client) doReg(ctx context.Context, url string, typ string, acct *Account) (*Account, error) {
req := struct {
Resource string `json:"resource"`
Contact []string `json:"contact,omitempty"`
Agreement string `json:"agreement,omitempty"`
}{
Resource: typ,
}
if acct != nil {
req.Contact = acct.Contact
req.Agreement = acct.AgreedTerms
}
res, err := c.post(ctx, nil, url, req, wantStatus(
http.StatusOK, // updates and deletes
http.StatusCreated, // new account creation
http.StatusAccepted, // Let's Encrypt divergent implementation
))
if err != nil {
return nil, err
}
defer res.Body.Close()
var v struct {
Contact []string
Agreement string
Authorizations string
Certificates string
}
if err := json.NewDecoder(res.Body).Decode(&v); err != nil {
return nil, fmt.Errorf("acme: invalid response: %v", err)
}
var tos string
if v := linkHeader(res.Header, "terms-of-service"); len(v) > 0 {
tos = v[0]
}
var authz string
if v := linkHeader(res.Header, "next"); len(v) > 0 {
authz = v[0]
}
return &Account{
URI: res.Header.Get("Location"),
Contact: v.Contact,
AgreedTerms: v.Agreement,
CurrentTerms: tos,
Authz: authz,
Authorizations: v.Authorizations,
Certificates: v.Certificates,
}, nil
}
// popNonce returns a nonce value previously stored with c.addNonce
// or fetches a fresh one from c.dir.NonceURL.
// If NonceURL is empty, it first tries c.directoryURL() and, failing that,
// the provided url.
func (c *Client) popNonce(ctx context.Context, url string) (string, error) {
c.noncesMu.Lock()
defer c.noncesMu.Unlock()
if len(c.nonces) == 0 {
if c.dir != nil && c.dir.NonceURL != "" {
return c.fetchNonce(ctx, c.dir.NonceURL)
}
dirURL := c.directoryURL()
v, err := c.fetchNonce(ctx, dirURL)
if err != nil && url != dirURL {
v, err = c.fetchNonce(ctx, url)
}
return v, err
}
var nonce string
for nonce = range c.nonces {
delete(c.nonces, nonce)
break
}
return nonce, nil
}
// clearNonces clears any stored nonces
func (c *Client) clearNonces() {
c.noncesMu.Lock()
defer c.noncesMu.Unlock()
c.nonces = make(map[string]struct{})
}
// addNonce stores a nonce value found in h (if any) for future use.
func (c *Client) addNonce(h http.Header) {
v := nonceFromHeader(h)
if v == "" {
return
}
c.noncesMu.Lock()
defer c.noncesMu.Unlock()
if len(c.nonces) >= maxNonces {
return
}
if c.nonces == nil {
c.nonces = make(map[string]struct{})
}
c.nonces[v] = struct{}{}
}
func (c *Client) fetchNonce(ctx context.Context, url string) (string, error) {
r, err := http.NewRequest("HEAD", url, nil)
if err != nil {
return "", err
}
resp, err := c.doNoRetry(ctx, r)
if err != nil {
return "", err
}
defer resp.Body.Close()
nonce := nonceFromHeader(resp.Header)
if nonce == "" {
if resp.StatusCode > 299 {
return "", responseError(resp)
}
return "", errors.New("acme: nonce not found")
}
return nonce, nil
}
func nonceFromHeader(h http.Header) string {
return h.Get("Replay-Nonce")
}
func (c *Client) responseCert(ctx context.Context, res *http.Response, bundle bool) ([][]byte, error) {
b, err := ioutil.ReadAll(io.LimitReader(res.Body, maxCertSize+1))
if err != nil {
return nil, fmt.Errorf("acme: response stream: %v", err)
}
if len(b) > maxCertSize {
return nil, errors.New("acme: certificate is too big")
}
cert := [][]byte{b}
if !bundle {
return cert, nil
}
// Append CA chain cert(s).
// At least one is required according to the spec:
// https://tools.ietf.org/html/draft-ietf-acme-acme-03#section-6.3.1
up := linkHeader(res.Header, "up")
if len(up) == 0 {
return nil, errors.New("acme: rel=up link not found")
}
if len(up) > maxChainLen {
return nil, errors.New("acme: rel=up link is too large")
}
for _, url := range up {
cc, err := c.chainCert(ctx, url, 0)
if err != nil {
return nil, err
}
cert = append(cert, cc...)
}
return cert, nil
}
// chainCert fetches CA certificate chain recursively by following "up" links.
// Each recursive call increments the depth by 1, resulting in an error
// if the recursion level reaches maxChainLen.
//
// First chainCert call starts with depth of 0.
func (c *Client) chainCert(ctx context.Context, url string, depth int) ([][]byte, error) {
if depth >= maxChainLen {
return nil, errors.New("acme: certificate chain is too deep")
}
res, err := c.get(ctx, url, wantStatus(http.StatusOK))
if err != nil {
return nil, err
}
defer res.Body.Close()
b, err := ioutil.ReadAll(io.LimitReader(res.Body, maxCertSize+1))
if err != nil {
return nil, err
}
if len(b) > maxCertSize {
return nil, errors.New("acme: certificate is too big")
}
chain := [][]byte{b}
uplink := linkHeader(res.Header, "up")
if len(uplink) > maxChainLen {
return nil, errors.New("acme: certificate chain is too large")
}
for _, up := range uplink {
cc, err := c.chainCert(ctx, up, depth+1)
if err != nil {
return nil, err
}
chain = append(chain, cc...)
}
return chain, nil
}
// linkHeader returns URI-Reference values of all Link headers
// with relation-type rel.
// See https://tools.ietf.org/html/rfc5988#section-5 for details.
func linkHeader(h http.Header, rel string) []string {
var links []string
for _, v := range h["Link"] {
parts := strings.Split(v, ";")
for _, p := range parts {
p = strings.TrimSpace(p)
if !strings.HasPrefix(p, "rel=") {
continue
}
if v := strings.Trim(p[4:], `"`); v == rel {
links = append(links, strings.Trim(parts[0], "<>"))
}
}
}
return links
}
// keyAuth generates a key authorization string for a given token.
func keyAuth(pub crypto.PublicKey, token string) (string, error) {
th, err := JWKThumbprint(pub)
if err != nil {
return "", err
}
return fmt.Sprintf("%s.%s", token, th), nil
}
// defaultTLSChallengeCertTemplate is a template used to create challenge certs for TLS challenges.
func defaultTLSChallengeCertTemplate() *x509.Certificate {
return &x509.Certificate{
SerialNumber: big.NewInt(1),
NotBefore: time.Now(),
NotAfter: time.Now().Add(24 * time.Hour),
BasicConstraintsValid: true,
KeyUsage: x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature,
ExtKeyUsage: []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
}
}
// tlsChallengeCert creates a temporary certificate for TLS-SNI challenges
// with the given SANs and auto-generated public/private key pair.
// The Subject Common Name is set to the first SAN to aid debugging.
// To create a cert with a custom key pair, specify WithKey option.
func tlsChallengeCert(san []string, opt []CertOption) (tls.Certificate, error) {
var key crypto.Signer
tmpl := defaultTLSChallengeCertTemplate()
for _, o := range opt {
switch o := o.(type) {
case *certOptKey:
if key != nil {
return tls.Certificate{}, errors.New("acme: duplicate key option")
}
key = o.key
case *certOptTemplate:
t := *(*x509.Certificate)(o) // shallow copy is ok
tmpl = &t
default:
// package's fault, if we let this happen:
panic(fmt.Sprintf("unsupported option type %T", o))
}
}
if key == nil {
var err error
if key, err = ecdsa.GenerateKey(elliptic.P256(), rand.Reader); err != nil {
return tls.Certificate{}, err
}
}
tmpl.DNSNames = san
if len(san) > 0 {
tmpl.Subject.CommonName = san[0]
}
der, err := x509.CreateCertificate(rand.Reader, tmpl, tmpl, key.Public(), key)
if err != nil {
return tls.Certificate{}, err
}
return tls.Certificate{
Certificate: [][]byte{der},
PrivateKey: key,
}, nil
}
// encodePEM returns b encoded as PEM with block of type typ.
func encodePEM(typ string, b []byte) []byte {
pb := &pem.Block{Type: typ, Bytes: b}
return pem.EncodeToMemory(pb)
}
// timeNow is useful for testing for fixed current time.
var timeNow = time.Now