feat: support Automatically install TLS certificates from Let's Encrypt. (#205)

* feat: support Automatically install TLS certificates from Let's Encrypt.

* refactor: update tls server.

* fix: missing tls package.

* fix: drop 1.6.x support

* docs: update readme.

* fix: listen tcp :443: bind: permission denied

.drone.yml

@@ -78,4 +78,3 @@ matrix:
   GO_VERSION:
     - 1.8.0
     - 1.7.5
-    - 1.6.4

.drone.yml.sig

@@ -1 +1 @@
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README.md

@@ -52,13 +52,14 @@ A push notification micro server using [Gin](https://github.com/gin-gonic/gin) f
 * Support for HTTP proxy to Google server (GCM).
 * Support retry send notification if server response is fail.
 * Support expose [prometheus](https://prometheus.io/) metrics.
+* Support install TLS certificates from [Let's Encrypt](https://letsencrypt.org/) automatically.
 
 See the [YAML config example](config/config.yml):
 
 [embedmd]:# (config/config.yml yaml)
 ```yaml
 core:
-  port: "8088"
+  port: "8088" # ignore this port number if auto_tls is enabled (listen 443).
   worker_num: 0 # default worker number is runtime.NumCPU()
   queue_num: 0 # default queue number is 8192
   max_notification: 100
@@ -71,6 +72,10 @@ core:
     enabled: false
     path: "gorush.pid"
     override: true
+  auto_tls:
+    enabled: false # Automatically install TLS certificates from Let's Encrypt.
+    folder: ".cache" # folder for storing TLS certificates
+    host: "" # which domains the Let's Encrypt will attempt
 
 api:
   push_uri: "/api/push"
@@ -233,7 +238,7 @@ $ gorush -c config.yml
 Get go status of api server using [httpie](https://github.com/jkbrzt/httpie) tool:
 
 ```bash
-$ http -v --verify=no --json GET https://localhost:8088/api/stat/go
+$ http -v --verify=no --json GET http://localhost:8088/api/stat/go
 ```
 
 ## Web API

config/config.go

@@ -29,6 +29,14 @@ type SectionCore struct {
 	KeyPath         string         `yaml:"key_path"`
 	HTTPProxy       string         `yaml:"http_proxy"`
 	PID             SectionPID     `yaml:"pid"`
+	AutoTLS         SectionAutoTLS `yaml:"auto_tls"`
+}
+
+// SectionAutoTLS support Let's Encrypt setting.
+type SectionAutoTLS struct {
+	Enabled bool   `yaml:"enabled"`
+	Folder  string `yaml:"folder"`
+	Host    string `yaml:"host"`
 }
 
 // SectionAPI is sub section of config.
@@ -123,6 +131,9 @@ func BuildDefaultPushConf() ConfYaml {
 	conf.Core.PID.Enabled = false
 	conf.Core.PID.Path = "gorush.pid"
 	conf.Core.PID.Override = false
+	conf.Core.AutoTLS.Enabled = false
+	conf.Core.AutoTLS.Folder = ".cache"
+	conf.Core.AutoTLS.Host = ""
 
 	// Api
 	conf.API.PushURI = "/api/push"

config/config.yml

@@ -1,5 +1,5 @@
 core:
-  port: "8088"
+  port: "8088" # ignore this port number if auto_tls is enabled (listen 443).
   worker_num: 0 # default worker number is runtime.NumCPU()
   queue_num: 0 # default queue number is 8192
   max_notification: 100
@@ -12,6 +12,10 @@ core:
     enabled: false
     path: "gorush.pid"
     override: true
+  auto_tls:
+    enabled: false # Automatically install TLS certificates from Let's Encrypt.
+    folder: ".cache" # folder for storing TLS certificates
+    host: "" # which domains the Let's Encrypt will attempt
 
 api:
   push_uri: "/api/push"

config/config_test.go

@@ -68,6 +68,9 @@ func (suite *ConfigTestSuite) TestValidateConfDefault() {
 	assert.Equal(suite.T(), false, suite.ConfGorushDefault.Core.PID.Enabled)
 	assert.Equal(suite.T(), "gorush.pid", suite.ConfGorushDefault.Core.PID.Path)
 	assert.Equal(suite.T(), false, suite.ConfGorushDefault.Core.PID.Override)
+	assert.Equal(suite.T(), false, suite.ConfGorushDefault.Core.AutoTLS.Enabled)
+	assert.Equal(suite.T(), ".cache", suite.ConfGorushDefault.Core.AutoTLS.Folder)
+	assert.Equal(suite.T(), "", suite.ConfGorushDefault.Core.AutoTLS.Host)
 
 	// Api
 	assert.Equal(suite.T(), "/api/push", suite.ConfGorushDefault.API.PushURI)
@@ -124,6 +127,9 @@ func (suite *ConfigTestSuite) TestValidateConf() {
 	assert.Equal(suite.T(), false, suite.ConfGorush.Core.PID.Enabled)
 	assert.Equal(suite.T(), "gorush.pid", suite.ConfGorush.Core.PID.Path)
 	assert.Equal(suite.T(), true, suite.ConfGorush.Core.PID.Override)
+	assert.Equal(suite.T(), false, suite.ConfGorush.Core.AutoTLS.Enabled)
+	assert.Equal(suite.T(), ".cache", suite.ConfGorush.Core.AutoTLS.Folder)
+	assert.Equal(suite.T(), "", suite.ConfGorush.Core.AutoTLS.Host)
 
 	// Api
 	assert.Equal(suite.T(), "/api/push", suite.ConfGorush.API.PushURI)

gorush/server.go

@@ -1,12 +1,14 @@
 package gorush
 
 import (
+	"crypto/tls"
 	"fmt"
 	"net/http"
 
 	"github.com/gin-gonic/gin"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
+	"golang.org/x/crypto/acme/autocert"
 	api "gopkg.in/appleboy/gin-status-api.v1"
 )
 
@@ -70,6 +72,20 @@ func metricsHandler(c *gin.Context) {
 	promhttp.Handler().ServeHTTP(c.Writer, c.Request)
 }
 
+func autoTLSServer() *http.Server {
+	m := autocert.Manager{
+		Prompt:     autocert.AcceptTOS,
+		HostPolicy: autocert.HostWhitelist(PushConf.Core.AutoTLS.Host),
+		Cache:      autocert.DirCache(PushConf.Core.AutoTLS.Folder),
+	}
+
+	return &http.Server{
+		Addr:      ":https",
+		TLSConfig: &tls.Config{GetCertificate: m.GetCertificate},
+		Handler:   routerEngine(),
+	}
+}
+
 func routerEngine() *gin.Engine {
 	// set server mode
 	gin.SetMode(PushConf.Core.Mode)

gorush/server_test.go

@@ -63,6 +63,17 @@ func TestRunTLSServer(t *testing.T) {
 	gofight.TestRequest(t, "https://localhost:8087/api/stat/go")
 }
 
+func TestRunAutoTLSServer(t *testing.T) {
+	initTest()
+	PushConf.Core.AutoTLS.Enabled = true
+	go func() {
+		assert.NoError(t, RunHTTPServer())
+	}()
+	// have to wait for the goroutine to start and run the server
+	// otherwise the main thread will complete
+	time.Sleep(5 * time.Millisecond)
+}
+
 func TestLoadTLSCertError(t *testing.T) {
 	initTest()
 

gorush/server_unix.go

@@ -10,10 +10,10 @@ import (
 )
 
 // RunHTTPServer provide run http or https protocol.
-func RunHTTPServer() error {
+func RunHTTPServer() (err error) {
-	var err error
+	if PushConf.Core.AutoTLS.Enabled {
-
+		err = gracehttp.Serve(autoTLSServer())
-	if PushConf.Core.SSL && PushConf.Core.CertPath != "" && PushConf.Core.KeyPath != "" {
+	} else if PushConf.Core.SSL && PushConf.Core.CertPath != "" && PushConf.Core.KeyPath != "" {
 		config := &tls.Config{
 			MinVersion: tls.VersionTLS10,
 		}
@@ -41,5 +41,5 @@ func RunHTTPServer() error {
 		})
 	}
 
-	return err
+	return
 }

gorush/server_windows.go

@@ -7,14 +7,15 @@ import (
 )
 
 // RunHTTPServer provide run http or https protocol.
-func RunHTTPServer() error {
+func RunHTTPServer() (err error) {
-	var err error
+	if PushConf.Core.AutoTLS.Enabled {
-
+		s := autoTLSServer()
-	if PushConf.Core.SSL && PushConf.Core.CertPath != "" && PushConf.Core.KeyPath != "" {
+		err = s.ListenAndServeTLS("", "")
+	} else if PushConf.Core.SSL && PushConf.Core.CertPath != "" && PushConf.Core.KeyPath != "" {
 		err = http.ListenAndServeTLS(":"+PushConf.Core.Port, PushConf.Core.CertPath, PushConf.Core.KeyPath, routerEngine())
 	} else {
 		err = http.ListenAndServe(":"+PushConf.Core.Port, routerEngine())
 	}
 
-	return err
+	return
 }

vendor/golang.org/x/crypto/acme/acme.go

@@ -0,0 +1,999 @@
+// 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.
+// See https://tools.ietf.org/html/draft-ietf-acme-acme-02 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 (
+	"bytes"
+	"context"
+	"crypto"
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"crypto/rand"
+	"crypto/sha256"
+	"crypto/tls"
+	"crypto/x509"
+	"encoding/base64"
+	"encoding/hex"
+	"encoding/json"
+	"encoding/pem"
+	"errors"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"math/big"
+	"net/http"
+	"strconv"
+	"strings"
+	"sync"
+	"time"
+
+	"golang.org/x/net/context/ctxhttp"
+)
+
+// LetsEncryptURL is the Directory endpoint of Let's Encrypt CA.
+const LetsEncryptURL = "https://acme-v01.api.letsencrypt.org/directory"
+
+const (
+	maxChainLen = 5       // max depth and breadth of a certificate chain
+	maxCertSize = 1 << 20 // max size of a certificate, in bytes
+
+	// Max number of collected nonces kept in memory.
+	// Expect usual peak of 1 or 2.
+	maxNonces = 100
+)
+
+// CertOption is an optional argument type for Client methods which manipulate
+// certificate data.
+type CertOption interface {
+	privateCertOpt()
+}
+
+// WithKey creates an option holding a private/public key pair.
+// The private part signs a certificate, and the public part represents the signee.
+func WithKey(key crypto.Signer) CertOption {
+	return &certOptKey{key}
+}
+
+type certOptKey struct {
+	key crypto.Signer
+}
+
+func (*certOptKey) privateCertOpt() {}
+
+// WithTemplate creates an option for specifying a certificate template.
+// See x509.CreateCertificate for template usage details.
+//
+// In TLSSNIxChallengeCert methods, the template is also used as parent,
+// resulting in a self-signed certificate.
+// The DNSNames field of t is always overwritten for tls-sni challenge certs.
+func WithTemplate(t *x509.Certificate) CertOption {
+	return (*certOptTemplate)(t)
+}
+
+type certOptTemplate x509.Certificate
+
+func (*certOptTemplate) privateCertOpt() {}
+
+// 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.
+	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
+
+	dirMu sync.Mutex // guards writes to dir
+	dir   *Directory // cached result of Client's Discover method
+
+	noncesMu sync.Mutex
+	nonces   map[string]struct{} // nonces collected from previous responses
+}
+
+// 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.dirMu.Lock()
+	defer c.dirMu.Unlock()
+	if c.dir != nil {
+		return *c.dir, nil
+	}
+
+	dirURL := c.DirectoryURL
+	if dirURL == "" {
+		dirURL = LetsEncryptURL
+	}
+	res, err := ctxhttp.Get(ctx, c.HTTPClient, dirURL)
+	if err != nil {
+		return Directory{}, err
+	}
+	defer res.Body.Close()
+	c.addNonce(res.Header)
+	if res.StatusCode != http.StatusOK {
+		return Directory{}, responseError(res)
+	}
+
+	var v struct {
+		Reg    string `json:"new-reg"`
+		Authz  string `json:"new-authz"`
+		Cert   string `json:"new-cert"`
+		Revoke string `json:"revoke-cert"`
+		Meta   struct {
+			Terms   string   `json:"terms-of-service"`
+			Website string   `json:"website"`
+			CAA     []string `json:"caa-identities"`
+		}
+	}
+	if json.NewDecoder(res.Body).Decode(&v); err != nil {
+		return Directory{}, err
+	}
+	c.dir = &Directory{
+		RegURL:    v.Reg,
+		AuthzURL:  v.Authz,
+		CertURL:   v.Cert,
+		RevokeURL: v.Revoke,
+		Terms:     v.Meta.Terms,
+		Website:   v.Meta.Website,
+		CAA:       v.Meta.CAA,
+	}
+	return *c.dir, nil
+}
+
+// CreateCert requests a new certificate using the Certificate Signing Request csr encoded in DER format.
+// 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 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.postJWS(ctx, c.Key, c.dir.CertURL, req)
+	if err != nil {
+		return nil, "", err
+	}
+	defer res.Body.Close()
+	if res.StatusCode != http.StatusCreated {
+		return nil, "", responseError(res)
+	}
+
+	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 := responseCert(ctx, c.HTTPClient, 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.
+//
+// The returned value will also contain the CA (issuer) certificate if the bundle argument is true.
+//
+// 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) {
+	for {
+		res, err := ctxhttp.Get(ctx, c.HTTPClient, url)
+		if err != nil {
+			return nil, err
+		}
+		defer res.Body.Close()
+		if res.StatusCode == http.StatusOK {
+			return responseCert(ctx, c.HTTPClient, res, bundle)
+		}
+		if res.StatusCode > 299 {
+			return nil, responseError(res)
+		}
+		d := retryAfter(res.Header.Get("retry-after"), 3*time.Second)
+		select {
+		case <-time.After(d):
+			// retry
+		case <-ctx.Done():
+			return nil, ctx.Err()
+		}
+	}
+}
+
+// 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 {
+	if _, err := c.Discover(ctx); err != nil {
+		return err
+	}
+
+	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),
+	}
+	if key == nil {
+		key = c.Key
+	}
+	res, err := c.postJWS(ctx, key, c.dir.RevokeURL, body)
+	if err != nil {
+		return err
+	}
+	defer res.Body.Close()
+	if res.StatusCode != http.StatusOK {
+		return responseError(res)
+	}
+	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 registration by following the "new-reg" flow.
+// It returns registered account. The a argument 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.
+func (c *Client) Register(ctx context.Context, a *Account, prompt func(tosURL string) bool) (*Account, error) {
+	if _, err := c.Discover(ctx); err != nil {
+		return nil, err
+	}
+
+	var err error
+	if a, err = c.doReg(ctx, c.dir.RegURL, "new-reg", a); 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 registration.
+// The url argument is an Account URI.
+func (c *Client) GetReg(ctx context.Context, url string) (*Account, error) {
+	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.
+func (c *Client) UpdateReg(ctx context.Context, a *Account) (*Account, error) {
+	uri := a.URI
+	a, err := c.doReg(ctx, uri, "reg", a)
+	if err != nil {
+		return nil, err
+	}
+	a.URI = uri
+	return a, nil
+}
+
+// Authorize performs the initial step in an authorization 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.
+//
+// If an authorization has been previously granted, the CA may return
+// a valid authorization (Authorization.Status is StatusValid). If so, the caller
+// need not fulfill any challenge and can proceed to requesting a certificate.
+func (c *Client) Authorize(ctx context.Context, domain 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: "dns", Value: domain},
+	}
+	res, err := c.postJWS(ctx, c.Key, c.dir.AuthzURL, req)
+	if err != nil {
+		return nil, err
+	}
+	defer res.Body.Close()
+	if res.StatusCode != http.StatusCreated {
+		return nil, responseError(res)
+	}
+
+	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) {
+	res, err := ctxhttp.Get(ctx, c.HTTPClient, url)
+	if err != nil {
+		return nil, err
+	}
+	defer res.Body.Close()
+	if res.StatusCode != http.StatusOK && res.StatusCode != http.StatusAccepted {
+		return nil, responseError(res)
+	}
+	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 method 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 {
+	req := struct {
+		Resource string `json:"resource"`
+		Status   string `json:"status"`
+		Delete   bool   `json:"delete"`
+	}{
+		Resource: "authz",
+		Status:   "deactivated",
+		Delete:   true,
+	}
+	res, err := c.postJWS(ctx, c.Key, url, req)
+	if err != nil {
+		return err
+	}
+	defer res.Body.Close()
+	if res.StatusCode != http.StatusOK {
+		return responseError(res)
+	}
+	return nil
+}
+
+// WaitAuthorization polls an authorization at the given URL
+// until it is in one of the final states, StatusValid or StatusInvalid,
+// 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 ErrAuthorizationFailed.
+func (c *Client) WaitAuthorization(ctx context.Context, url string) (*Authorization, error) {
+	var count int
+	sleep := func(v string, inc int) error {
+		count += inc
+		d := backoff(count, 10*time.Second)
+		d = retryAfter(v, d)
+		wakeup := time.NewTimer(d)
+		defer wakeup.Stop()
+		select {
+		case <-ctx.Done():
+			return ctx.Err()
+		case <-wakeup.C:
+			return nil
+		}
+	}
+
+	for {
+		res, err := ctxhttp.Get(ctx, c.HTTPClient, url)
+		if err != nil {
+			return nil, err
+		}
+		retry := res.Header.Get("retry-after")
+		if res.StatusCode != http.StatusOK && res.StatusCode != http.StatusAccepted {
+			res.Body.Close()
+			if err := sleep(retry, 1); err != nil {
+				return nil, err
+			}
+			continue
+		}
+		var raw wireAuthz
+		err = json.NewDecoder(res.Body).Decode(&raw)
+		res.Body.Close()
+		if err != nil {
+			if err := sleep(retry, 0); err != nil {
+				return nil, err
+			}
+			continue
+		}
+		if raw.Status == StatusValid {
+			return raw.authorization(url), nil
+		}
+		if raw.Status == StatusInvalid {
+			return nil, ErrAuthorizationFailed
+		}
+		if err := sleep(retry, 0); err != nil {
+			return nil, err
+		}
+	}
+}
+
+// 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) {
+	res, err := ctxhttp.Get(ctx, c.HTTPClient, url)
+	if err != nil {
+		return nil, err
+	}
+	defer res.Body.Close()
+	if res.StatusCode != http.StatusOK && res.StatusCode != http.StatusAccepted {
+		return nil, responseError(res)
+	}
+	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) {
+	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.postJWS(ctx, c.Key, chal.URI, req)
+	if err != nil {
+		return nil, err
+	}
+	defer res.Body.Close()
+	// Note: the protocol specifies 200 as the expected response code, but
+	// letsencrypt seems to be returning 202.
+	if res.StatusCode != http.StatusOK && res.StatusCode != http.StatusAccepted {
+		return nil, responseError(res)
+	}
+
+	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.
+// Servers can present the certificate to validate the challenge and prove control
+// over a domain name.
+//
+// The implementation is incomplete in that the returned value is a single certificate,
+// computed only for Z0 of the key authorization. ACME CAs are expected to update
+// their implementations to use the newer version, TLS-SNI-02.
+// For more details on TLS-SNI-01 see https://tools.ietf.org/html/draft-ietf-acme-acme-01#section-7.3.
+//
+// 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 of the client hello matches exactly the returned name value.
+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.
+// Servers can present the certificate to validate the challenge and prove control
+// over a domain name. For more details on TLS-SNI-02 see
+// https://tools.ietf.org/html/draft-ietf-acme-acme-03#section-7.3.
+//
+// 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 client hello matches exactly the returned name value.
+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
+}
+
+// doReg sends all types of registration requests.
+// 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.postJWS(ctx, c.Key, url, req)
+	if err != nil {
+		return nil, err
+	}
+	defer res.Body.Close()
+	if res.StatusCode < 200 || res.StatusCode > 299 {
+		return nil, responseError(res)
+	}
+
+	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
+}
+
+// postJWS signs the body with the given key and POSTs it to the provided url.
+// The body argument must be JSON-serializable.
+func (c *Client) postJWS(ctx context.Context, key crypto.Signer, url string, body interface{}) (*http.Response, error) {
+	nonce, err := c.popNonce(ctx, url)
+	if err != nil {
+		return nil, err
+	}
+	b, err := jwsEncodeJSON(body, key, nonce)
+	if err != nil {
+		return nil, err
+	}
+	res, err := ctxhttp.Post(ctx, c.HTTPClient, url, "application/jose+json", bytes.NewReader(b))
+	if err != nil {
+		return nil, err
+	}
+	c.addNonce(res.Header)
+	return res, nil
+}
+
+// popNonce returns a nonce value previously stored with c.addNonce
+// or fetches a fresh one from the given URL.
+func (c *Client) popNonce(ctx context.Context, url string) (string, error) {
+	c.noncesMu.Lock()
+	defer c.noncesMu.Unlock()
+	if len(c.nonces) == 0 {
+		return fetchNonce(ctx, c.HTTPClient, url)
+	}
+	var nonce string
+	for nonce = range c.nonces {
+		delete(c.nonces, nonce)
+		break
+	}
+	return nonce, nil
+}
+
+// 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 fetchNonce(ctx context.Context, client *http.Client, url string) (string, error) {
+	resp, err := ctxhttp.Head(ctx, client, url)
+	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")
+	}