diff --git a/Gopkg.lock b/Gopkg.lock
index 7a46e35909..28139ac62c 100644
--- a/Gopkg.lock
+++ b/Gopkg.lock
@@ -301,14 +301,14 @@
 
 [[projects]]
   branch = "master"
-  digest = "1:507fa82feeba6c3651d3cfb7593a498144ae6455e1b00dde2e0c344cdfdc9c4d"
+  digest = "1:9ebbac90dda5bf921f6243b64d5abd0674ada63cdee056ff671f8658a00034ab"
   name = "golang.org/x/crypto"
   packages = [
     "acme",
     "acme/autocert",
   ]
   pruneopts = "UT"
-  revision = "1a580b3eff7814fc9b40602fd35256c63b50f491"
+  revision = "cbcb750295291b33242907a04be40e80801d0cfc"
 
 [[projects]]
   branch = "master"
@@ -429,6 +429,7 @@
     "github.com/satori/go.uuid",
     "github.com/spf13/cobra",
     "github.com/stretchr/testify/assert",
+    "golang.org/x/crypto/acme",
     "golang.org/x/crypto/acme/autocert",
     "golang.org/x/net/context",
     "google.golang.org/grpc",
diff --git a/main.go b/main.go
index 2b7789e193..439cf52499 100644
--- a/main.go
+++ b/main.go
@@ -38,6 +38,7 @@ import (
 	"github.com/rs/zerolog/log"
 	"github.com/satori/go.uuid"
 	"github.com/spf13/cobra"
+	"golang.org/x/crypto/acme"
 	"golang.org/x/crypto/acme/autocert"
 	"google.golang.org/grpc"
 	"google.golang.org/grpc/credentials"
@@ -552,6 +553,9 @@ func getTLSConfig() (*tls.Config, error) {
 				}
 				return certManager.GetCertificate(hello)
 			},
+			NextProtos: []string{
+				"h2", "http/1.1", acme.ALPNProto,
+			},
 		}, nil
 
 	} else if tlsEnabled {
diff --git a/vendor/golang.org/x/crypto/acme/acme.go b/vendor/golang.org/x/crypto/acme/acme.go
index 1f4fb69edd..00ee955503 100644
--- a/vendor/golang.org/x/crypto/acme/acme.go
+++ b/vendor/golang.org/x/crypto/acme/acme.go
@@ -14,7 +14,6 @@
 package acme
 
 import (
-	"bytes"
 	"context"
 	"crypto"
 	"crypto/ecdsa"
@@ -23,6 +22,8 @@ import (
 	"crypto/sha256"
 	"crypto/tls"
 	"crypto/x509"
+	"crypto/x509/pkix"
+	"encoding/asn1"
 	"encoding/base64"
 	"encoding/hex"
 	"encoding/json"
@@ -33,14 +34,26 @@ import (
 	"io/ioutil"
 	"math/big"
 	"net/http"
-	"strconv"
 	"strings"
 	"sync"
 	"time"
 )
 
-// LetsEncryptURL is the Directory endpoint of Let's Encrypt CA.
-const LetsEncryptURL = "https://acme-v01.api.letsencrypt.org/directory"
+const (
+	// LetsEncryptURL is the Directory endpoint of Let's Encrypt CA.
+	LetsEncryptURL = "https://acme-v01.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"
+)
+
+// idPeACMEIdentifierV1 is the OID for the ACME extension for the TLS-ALPN challenge.
+var idPeACMEIdentifierV1 = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 1, 30, 1}
 
 const (
 	maxChainLen = 5       // max depth and breadth of a certificate chain
@@ -64,6 +77,10 @@ const (
 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
@@ -76,6 +93,22 @@ type Client struct {
 	// 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
+
 	dirMu sync.Mutex // guards writes to dir
 	dir   *Directory // cached result of Client's Discover method
 
@@ -95,19 +128,12 @@ func (c *Client) Discover(ctx context.Context) (Directory, error) {
 		return *c.dir, nil
 	}
 
-	dirURL := c.DirectoryURL
-	if dirURL == "" {
-		dirURL = LetsEncryptURL
-	}
-	res, err := c.get(ctx, dirURL)
+	res, err := c.get(ctx, c.directoryURL(), wantStatus(http.StatusOK))
 	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"`
@@ -135,6 +161,13 @@ func (c *Client) Discover(ctx context.Context) (Directory, error) {
 	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.
 // The exp argument indicates the desired certificate validity duration. CA may issue a certificate
 // with a different duration.
@@ -166,14 +199,11 @@ func (c *Client) CreateCert(ctx context.Context, csr []byte, exp time.Duration,
 		req.NotAfter = now.Add(exp).Format(time.RFC3339)
 	}
 
-	res, err := c.retryPostJWS(ctx, c.Key, c.dir.CertURL, req)
+	res, err := c.post(ctx, c.Key, c.dir.CertURL, req, wantStatus(http.StatusCreated))
 	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 {
@@ -196,26 +226,11 @@ func (c *Client) CreateCert(ctx context.Context, csr []byte, exp time.Duration,
 // 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 := c.get(ctx, url)
-		if err != nil {
-			return nil, err
-		}
-		defer res.Body.Close()
-		if res.StatusCode == http.StatusOK {
-			return c.responseCert(ctx, 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()
-		}
+	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.
@@ -241,14 +256,11 @@ func (c *Client) RevokeCert(ctx context.Context, key crypto.Signer, cert []byte,
 	if key == nil {
 		key = c.Key
 	}
-	res, err := c.retryPostJWS(ctx, key, c.dir.RevokeURL, body)
+	res, err := c.post(ctx, key, c.dir.RevokeURL, body, wantStatus(http.StatusOK))
 	if err != nil {
 		return err
 	}
 	defer res.Body.Close()
-	if res.StatusCode != http.StatusOK {
-		return responseError(res)
-	}
 	return nil
 }
 
@@ -314,6 +326,20 @@ func (c *Client) UpdateReg(ctx context.Context, a *Account) (*Account, error) {
 // 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) {
+	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
 	}
@@ -327,16 +353,13 @@ func (c *Client) Authorize(ctx context.Context, domain string) (*Authorization,
 		Identifier authzID `json:"identifier"`
 	}{
 		Resource:   "new-authz",
-		Identifier: authzID{Type: "dns", Value: domain},
+		Identifier: authzID{Type: typ, Value: val},
 	}
-	res, err := c.retryPostJWS(ctx, c.Key, c.dir.AuthzURL, req)
+	res, err := c.post(ctx, c.Key, c.dir.AuthzURL, req, wantStatus(http.StatusCreated))
 	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 {
@@ -353,14 +376,11 @@ func (c *Client) Authorize(ctx context.Context, domain string) (*Authorization,
 // 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 := c.get(ctx, url)
+	res, err := c.get(ctx, url, wantStatus(http.StatusOK, http.StatusAccepted))
 	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)
@@ -387,14 +407,11 @@ func (c *Client) RevokeAuthorization(ctx context.Context, url string) error {
 		Status:   "deactivated",
 		Delete:   true,
 	}
-	res, err := c.retryPostJWS(ctx, c.Key, url, req)
+	res, err := c.post(ctx, c.Key, url, req, wantStatus(http.StatusOK))
 	if err != nil {
 		return err
 	}
 	defer res.Body.Close()
-	if res.StatusCode != http.StatusOK {
-		return responseError(res)
-	}
 	return nil
 }
 
@@ -406,44 +423,42 @@ func (c *Client) RevokeAuthorization(ctx context.Context, url string) error {
 // 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) {
-	sleep := sleeper(ctx)
 	for {
-		res, err := c.get(ctx, url)
+		res, err := c.get(ctx, url, wantStatus(http.StatusOK, http.StatusAccepted))
 		if err != nil {
 			return nil, err
 		}
-		if res.StatusCode >= 400 && res.StatusCode <= 499 {
-			// Non-retriable error. For instance, Let's Encrypt may return 404 Not Found
-			// when requesting an expired authorization.
-			defer res.Body.Close()
-			return nil, responseError(res)
-		}
 
-		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 {
+		switch {
+		case err != nil:
+			// Skip and retry.
+		case raw.Status == StatusValid:
 			return raw.authorization(url), nil
-		}
-		if raw.Status == StatusInvalid {
+		case raw.Status == StatusInvalid:
 			return nil, raw.error(url)
 		}
-		if err := sleep(retry, 0); err != nil {
-			return nil, err
+
+		// 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.
 		}
 	}
 }
@@ -452,14 +467,11 @@ func (c *Client) WaitAuthorization(ctx context.Context, url string) (*Authorizat
 //
 // A client typically polls a challenge status using this method.
 func (c *Client) GetChallenge(ctx context.Context, url string) (*Challenge, error) {
-	res, err := c.get(ctx, url)
+	res, err := c.get(ctx, url, wantStatus(http.StatusOK, http.StatusAccepted))
 	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)
@@ -486,16 +498,14 @@ func (c *Client) Accept(ctx context.Context, chal *Challenge) (*Challenge, error
 		Type:     chal.Type,
 		Auth:     auth,
 	}
-	res, err := c.retryPostJWS(ctx, c.Key, chal.URI, req)
+	res, err := c.post(ctx, c.Key, 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()
-	// 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 {
@@ -552,7 +562,7 @@ func (c *Client) HTTP01ChallengePath(token string) string {
 // 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.
+// the server name of the TLS ClientHello 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 {
@@ -579,7 +589,7 @@ func (c *Client) TLSSNI01ChallengeCert(token string, opt ...CertOption) (cert tl
 // 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.
+// the server name in the TLS ClientHello 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[:])
@@ -600,6 +610,52 @@ func (c *Client) TLSSNI02ChallengeCert(token string, opt ...CertOption) (cert tl
 	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:       idPeACMEIdentifierV1,
+		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 type of request is identified by typ argument, which is a "resource"
 // in the ACME spec terms.
@@ -619,14 +675,15 @@ func (c *Client) doReg(ctx context.Context, url string, typ string, acct *Accoun
 		req.Contact = acct.Contact
 		req.Agreement = acct.AgreedTerms
 	}
-	res, err := c.retryPostJWS(ctx, c.Key, url, req)
+	res, err := c.post(ctx, c.Key, 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()
-	if res.StatusCode < 200 || res.StatusCode > 299 {
-		return nil, responseError(res)
-	}
 
 	var v struct {
 		Contact        []string
@@ -656,66 +713,19 @@ func (c *Client) doReg(ctx context.Context, url string, typ string, acct *Accoun
 	}, nil
 }
 
-// retryPostJWS will retry calls to postJWS if there is a badNonce error,
-// clearing the stored nonces after each error.
-// If the response was 4XX-5XX, then responseError is called on the body,
-// the body is closed, and the error returned.
-func (c *Client) retryPostJWS(ctx context.Context, key crypto.Signer, url string, body interface{}) (*http.Response, error) {
-	sleep := sleeper(ctx)
-	for {
-		res, err := c.postJWS(ctx, key, url, body)
-		if err != nil {
-			return nil, err
-		}
-		// handle errors 4XX-5XX with responseError
-		if res.StatusCode >= 400 && res.StatusCode <= 599 {
-			err := responseError(res)
-			res.Body.Close()
-			// according to spec badNonce is urn:ietf:params:acme:error:badNonce
-			// however, acme servers in the wild return their version of the error
-			// https://tools.ietf.org/html/draft-ietf-acme-acme-02#section-5.4
-			if ae, ok := err.(*Error); ok && strings.HasSuffix(strings.ToLower(ae.ProblemType), ":badnonce") {
-				// clear any nonces that we might've stored that might now be
-				// considered bad
-				c.clearNonces()
-				retry := res.Header.Get("Retry-After")
-				if err := sleep(retry, 1); err != nil {
-					return nil, err
-				}
-				continue
-			}
-			return nil, err
-		}
-		return res, 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 := c.post(ctx, 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.
+// or fetches a fresh one from a URL by issuing a HEAD request.
+// It first tries c.directoryURL() and then the provided url if the former fails.
 func (c *Client) popNonce(ctx context.Context, url string) (string, error) {
 	c.noncesMu.Lock()
 	defer c.noncesMu.Unlock()
 	if len(c.nonces) == 0 {
-		return c.fetchNonce(ctx, url)
+		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 {
@@ -749,58 +759,12 @@ func (c *Client) addNonce(h http.Header) {
 	c.nonces[v] = struct{}{}
 }
 
-func (c *Client) httpClient() *http.Client {
-	if c.HTTPClient != nil {
-		return c.HTTPClient
-	}
-	return http.DefaultClient
-}
-
-func (c *Client) get(ctx context.Context, urlStr string) (*http.Response, error) {
-	req, err := http.NewRequest("GET", urlStr, nil)
-	if err != nil {
-		return nil, err
-	}
-	return c.do(ctx, req)
-}
-
-func (c *Client) head(ctx context.Context, urlStr string) (*http.Response, error) {
-	req, err := http.NewRequest("HEAD", urlStr, nil)
-	if err != nil {
-		return nil, err
-	}
-	return c.do(ctx, req)
-}
-
-func (c *Client) post(ctx context.Context, urlStr, contentType string, body io.Reader) (*http.Response, error) {
-	req, err := http.NewRequest("POST", urlStr, body)
-	if err != nil {
-		return nil, err
-	}
-	req.Header.Set("Content-Type", contentType)
-	return c.do(ctx, req)
-}
-
-func (c *Client) do(ctx context.Context, req *http.Request) (*http.Response, error) {
-	res, err := c.httpClient().Do(req.WithContext(ctx))
+func (c *Client) fetchNonce(ctx context.Context, url string) (string, error) {
+	r, err := http.NewRequest("HEAD", url, nil)
 	if err != nil {
-		select {
-		case <-ctx.Done():
-			// Prefer the unadorned context error.
-			// (The acme package had tests assuming this, previously from ctxhttp's
-			// behavior, predating net/http supporting contexts natively)
-			// TODO(bradfitz): reconsider this in the future. But for now this
-			// requires no test updates.
-			return nil, ctx.Err()
-		default:
-			return nil, err
-		}
+		return "", err
 	}
-	return res, nil
-}
-
-func (c *Client) fetchNonce(ctx context.Context, url string) (string, error) {
-	resp, err := c.head(ctx, url)
+	resp, err := c.doNoRetry(ctx, r)
 	if err != nil {
 		return "", err
 	}
@@ -852,24 +816,6 @@ func (c *Client) responseCert(ctx context.Context, res *http.Response, bundle bo
 	return cert, nil
 }
 
-// responseError creates an error of Error type from resp.
-func responseError(resp *http.Response) error {
-	// don't care if ReadAll returns an error:
-	// json.Unmarshal will fail in that case anyway
-	b, _ := ioutil.ReadAll(resp.Body)
-	e := &wireError{Status: resp.StatusCode}
-	if err := json.Unmarshal(b, e); err != nil {
-		// this is not a regular error response:
-		// populate detail with anything we received,
-		// e.Status will already contain HTTP response code value
-		e.Detail = string(b)
-		if e.Detail == "" {
-			e.Detail = resp.Status
-		}
-	}
-	return e.error(resp.Header)
-}
-
 // 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.
@@ -880,14 +826,11 @@ func (c *Client) chainCert(ctx context.Context, url string, depth int) ([][]byte
 		return nil, errors.New("acme: certificate chain is too deep")
 	}
 
-	res, err := c.get(ctx, url)
+	res, err := c.get(ctx, url, wantStatus(http.StatusOK))
 	if err != nil {
 		return nil, err
 	}
 	defer res.Body.Close()
-	if res.StatusCode != http.StatusOK {
-		return nil, responseError(res)
-	}
 	b, err := ioutil.ReadAll(io.LimitReader(res.Body, maxCertSize+1))
 	if err != nil {
 		return nil, err
@@ -932,65 +875,6 @@ func linkHeader(h http.Header, rel string) []string {
 	return links
 }
 
-// sleeper returns a function that accepts the Retry-After HTTP header value
-// and an increment that's used with backoff to increasingly sleep on
-// consecutive calls until the context is done. If the Retry-After header
-// cannot be parsed, then backoff is used with a maximum sleep time of 10
-// seconds.
-func sleeper(ctx context.Context) func(ra string, inc int) error {
-	var count int
-	return func(ra string, inc int) error {
-		count += inc
-		d := backoff(count, 10*time.Second)
-		d = retryAfter(ra, d)
-		wakeup := time.NewTimer(d)
-		defer wakeup.Stop()
-		select {
-		case <-ctx.Done():
-			return ctx.Err()
-		case <-wakeup.C:
-			return nil
-		}
-	}
-}
-
-// retryAfter parses a Retry-After HTTP header value,
-// trying to convert v into an int (seconds) or use http.ParseTime otherwise.
-// It returns d if v cannot be parsed.
-func retryAfter(v string, d time.Duration) time.Duration {
-	if i, err := strconv.Atoi(v); err == nil {
-		return time.Duration(i) * time.Second
-	}
-	t, err := http.ParseTime(v)
-	if err != nil {
-		return d
-	}
-	return t.Sub(timeNow())
-}
-
-// backoff computes a duration after which an n+1 retry iteration should occur
-// using truncated exponential backoff algorithm.
-//
-// The n argument is always bounded between 0 and 30.
-// The max argument defines upper bound for the returned value.
-func backoff(n int, max time.Duration) time.Duration {
-	if n < 0 {
-		n = 0
-	}
-	if n > 30 {
-		n = 30
-	}
-	var d time.Duration
-	if x, err := rand.Int(rand.Reader, big.NewInt(1000)); err == nil {
-		d = time.Duration(x.Int64()) * time.Millisecond
-	}
-	d += time.Duration(1<<uint(n)) * time.Second
-	if d > max {
-		return max
-	}
-	return d
-}
-
 // keyAuth generates a key authorization string for a given token.
 func keyAuth(pub crypto.PublicKey, token string) (string, error) {
 	th, err := JWKThumbprint(pub)
@@ -1000,15 +884,25 @@ func keyAuth(pub crypto.PublicKey, token string) (string, error) {
 	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 *x509.Certificate
-	)
+	var key crypto.Signer
+	tmpl := defaultTLSChallengeCertTemplate()
 	for _, o := range opt {
 		switch o := o.(type) {
 		case *certOptKey:
@@ -1017,7 +911,7 @@ func tlsChallengeCert(san []string, opt []CertOption) (tls.Certificate, error) {
 			}
 			key = o.key
 		case *certOptTemplate:
-			var t = *(*x509.Certificate)(o) // shallow copy is ok
+			t := *(*x509.Certificate)(o) // shallow copy is ok
 			tmpl = &t
 		default:
 			// package's fault, if we let this happen:
@@ -1030,16 +924,6 @@ func tlsChallengeCert(san []string, opt []CertOption) (tls.Certificate, error) {
 			return tls.Certificate{}, err
 		}
 	}
-	if tmpl == nil {
-		tmpl = &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},
-		}
-	}
 	tmpl.DNSNames = san
 	if len(san) > 0 {
 		tmpl.Subject.CommonName = san[0]
diff --git a/vendor/golang.org/x/crypto/acme/autocert/autocert.go b/vendor/golang.org/x/crypto/acme/autocert/autocert.go
index 263b291331..e562609cc7 100644
--- a/vendor/golang.org/x/crypto/acme/autocert/autocert.go
+++ b/vendor/golang.org/x/crypto/acme/autocert/autocert.go
@@ -32,6 +32,7 @@ import (
 	"time"
 
 	"golang.org/x/crypto/acme"
+	"golang.org/x/net/idna"
 )
 
 // createCertRetryAfter is how much time to wait before removing a failed state
@@ -44,7 +45,7 @@ var createCertRetryAfter = time.Minute
 var pseudoRand *lockedMathRand
 
 func init() {
-	src := mathrand.NewSource(timeNow().UnixNano())
+	src := mathrand.NewSource(time.Now().UnixNano())
 	pseudoRand = &lockedMathRand{rnd: mathrand.New(src)}
 }
 
@@ -62,14 +63,20 @@ 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.
+//
+// Note that all hosts will be converted to Punycode via idna.Lookup.ToASCII so that
+// Manager.GetCertificate can handle the Unicode IDN and mixedcase hosts correctly.
+// Invalid hosts will be silently ignored.
 func HostWhitelist(hosts ...string) HostPolicy {
 	whitelist := make(map[string]bool, len(hosts))
 	for _, h := range hosts {
-		whitelist[h] = true
+		if h, err := idna.Lookup.ToASCII(h); err == nil {
+			whitelist[h] = true
+		}
 	}
 	return func(_ context.Context, host string) error {
 		if !whitelist[host] {
-			return errors.New("acme/autocert: host not configured")
+			return fmt.Errorf("acme/autocert: host %q not configured in HostWhitelist", host)
 		}
 		return nil
 	}
@@ -81,9 +88,9 @@ func defaultHostPolicy(context.Context, string) error {
 }
 
 // Manager is a stateful certificate manager built on top of acme.Client.
-// It obtains and refreshes certificates automatically using "tls-sni-01",
-// "tls-sni-02" and "http-01" challenge types, as well as providing them
-// to a TLS server via tls.Config.
+// It obtains and refreshes certificates automatically using "tls-alpn-01",
+// "tls-sni-01", "tls-sni-02" and "http-01" challenge types,
+// as well as providing them to a TLS server via tls.Config.
 //
 // You must specify a cache implementation, such as DirCache,
 // to reuse obtained certificates across program restarts.
@@ -98,11 +105,11 @@ type Manager struct {
 	// 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.
+	// Cache optionally stores and retrieves previously-obtained certificates
+	// and other state. If nil, certs will only be cached for the lifetime of
+	// the Manager. Multiple Managers can share the same Cache.
 	//
-	// Manager passes the Cache certificates data encoded in PEM, with private/public
-	// parts combined in a single Cache.Put call, private key first.
+	// Using a persistent Cache, such as DirCache, is strongly recommended.
 	Cache Cache
 
 	// HostPolicy controls which domains the Manager will attempt
@@ -127,8 +134,10 @@ type Manager struct {
 
 	// 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.
+	// as directory endpoint. If the Client.Key is nil, a new ECDSA P-256 key is
+	// generated and, if Cache is not nil, stored in cache.
 	//
 	// Mutating the field after the first call of GetCertificate method will have no effect.
 	Client *acme.Client
@@ -140,22 +149,30 @@ type Manager struct {
 	// 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.
+	// ForceRSA used to make the Manager generate RSA certificates. It is now ignored.
 	//
-	// If false, a default is used. Currently the default
-	// is EC-based keys using the P-256 curve.
+	// Deprecated: the Manager will request the correct type of certificate based
+	// on what each client supports.
 	ForceRSA bool
 
+	// ExtraExtensions are used when generating a new CSR (Certificate Request),
+	// thus allowing customization of the resulting certificate.
+	// For instance, TLS Feature Extension (RFC 7633) can be used
+	// to prevent an OCSP downgrade attack.
+	//
+	// The field value is passed to crypto/x509.CreateCertificateRequest
+	// in the template's ExtraExtensions field as is.
+	ExtraExtensions []pkix.Extension
+
 	clientMu sync.Mutex
 	client   *acme.Client // initialized by acmeClient method
 
 	stateMu sync.Mutex
-	state   map[string]*certState // keyed by domain name
+	state   map[certKey]*certState
 
 	// renewal tracks the set of domains currently running renewal timers.
-	// It is keyed by domain name.
 	renewalMu sync.Mutex
-	renewal   map[string]*domainRenewal
+	renewal   map[certKey]*domainRenewal
 
 	// tokensMu guards the rest of the fields: tryHTTP01, certTokens and httpTokens.
 	tokensMu sync.RWMutex
@@ -167,21 +184,60 @@ type Manager struct {
 	// to be provisioned.
 	// The entries are stored for the duration of the authorization flow.
 	httpTokens map[string][]byte
-	// certTokens contains temporary certificates for tls-sni challenges
+	// certTokens contains temporary certificates for tls-sni and tls-alpn challenges
 	// and is keyed by token domain name, which matches server name of ClientHello.
-	// Keys always have ".acme.invalid" suffix.
+	// Keys always have ".acme.invalid" suffix for tls-sni. Otherwise, they are domain names
+	// for tls-alpn.
 	// The entries are stored for the duration of the authorization flow.
 	certTokens map[string]*tls.Certificate
+	// nowFunc, if not nil, returns the current time. This may be set for
+	// testing purposes.
+	nowFunc func() time.Time
+}
+
+// certKey is the key by which certificates are tracked in state, renewal and cache.
+type certKey struct {
+	domain  string // without trailing dot
+	isRSA   bool   // RSA cert for legacy clients (as opposed to default ECDSA)
+	isToken bool   // tls-based challenge token cert; key type is undefined regardless of isRSA
+}
+
+func (c certKey) String() string {
+	if c.isToken {
+		return c.domain + "+token"
+	}
+	if c.isRSA {
+		return c.domain + "+rsa"
+	}
+	return c.domain
+}
+
+// TLSConfig creates a new TLS config suitable for net/http.Server servers,
+// supporting HTTP/2 and the tls-alpn-01 ACME challenge type.
+func (m *Manager) TLSConfig() *tls.Config {
+	return &tls.Config{
+		GetCertificate: m.GetCertificate,
+		NextProtos: []string{
+			"h2", "http/1.1", // enable HTTP/2
+			acme.ALPNProto, // enable tls-alpn ACME challenges
+		},
+	}
 }
 
 // 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.
+// tls-alpn-01 and *.acme.invalid (tls-sni-01 and tls-sni-02) 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.
+//
+// If GetCertificate is used directly, instead of via Manager.TLSConfig, package users will
+// also have to add acme.ALPNProto to NextProtos for tls-alpn-01, or use HTTPHandler
+// for http-01. (The tls-sni-* challenges have been deprecated by popular ACME providers
+// due to security issues in the ecosystem.)
 func (m *Manager) GetCertificate(hello *tls.ClientHelloInfo) (*tls.Certificate, error) {
 	if m.Prompt == nil {
 		return nil, errors.New("acme/autocert: Manager.Prompt not set")
@@ -194,7 +250,17 @@ func (m *Manager) GetCertificate(hello *tls.ClientHelloInfo) (*tls.Certificate,
 	if !strings.Contains(strings.Trim(name, "."), ".") {
 		return nil, errors.New("acme/autocert: server name component count invalid")
 	}
-	if strings.ContainsAny(name, `/\`) {
+
+	// Note that this conversion is necessary because some server names in the handshakes
+	// started by some clients (such as cURL) are not converted to Punycode, which will
+	// prevent us from obtaining certificates for them. In addition, we should also treat
+	// example.com and EXAMPLE.COM as equivalent and return the same certificate for them.
+	// Fortunately, this conversion also helped us deal with this kind of mixedcase problems.
+	//
+	// Due to the "σςΣ" problem (see https://unicode.org/faq/idn.html#22), we can't use
+	// idna.Punycode.ToASCII (or just idna.ToASCII) here.
+	name, err := idna.Lookup.ToASCII(name)
+	if err != nil {
 		return nil, errors.New("acme/autocert: server name contains invalid character")
 	}
 
@@ -203,14 +269,17 @@ func (m *Manager) GetCertificate(hello *tls.ClientHelloInfo) (*tls.Certificate,
 	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Minute)
 	defer cancel()
 
-	// check whether this is a token cert requested for TLS-SNI challenge
-	if strings.HasSuffix(name, ".acme.invalid") {
+	// Check whether this is a token cert requested for TLS-SNI or TLS-ALPN challenge.
+	if wantsTokenCert(hello) {
 		m.tokensMu.RLock()
 		defer m.tokensMu.RUnlock()
+		// It's ok to use the same token cert key for both tls-sni and tls-alpn
+		// because there's always at most 1 token cert per on-going domain authorization.
+		// See m.verify for details.
 		if cert := m.certTokens[name]; cert != nil {
 			return cert, nil
 		}
-		if cert, err := m.cacheGet(ctx, name); err == nil {
+		if cert, err := m.cacheGet(ctx, certKey{domain: name, isToken: true}); err == nil {
 			return cert, nil
 		}
 		// TODO: cache error results?
@@ -218,8 +287,11 @@ func (m *Manager) GetCertificate(hello *tls.ClientHelloInfo) (*tls.Certificate,
 	}
 
 	// regular domain
-	name = strings.TrimSuffix(name, ".") // golang.org/issue/18114
-	cert, err := m.cert(ctx, name)
+	ck := certKey{
+		domain: strings.TrimSuffix(name, "."), // golang.org/issue/18114
+		isRSA:  !supportsECDSA(hello),
+	}
+	cert, err := m.cert(ctx, ck)
 	if err == nil {
 		return cert, nil
 	}
@@ -231,14 +303,71 @@ func (m *Manager) GetCertificate(hello *tls.ClientHelloInfo) (*tls.Certificate,
 	if err := m.hostPolicy()(ctx, name); err != nil {
 		return nil, err
 	}
-	cert, err = m.createCert(ctx, name)
+	cert, err = m.createCert(ctx, ck)
 	if err != nil {
 		return nil, err
 	}
-	m.cachePut(ctx, name, cert)
+	m.cachePut(ctx, ck, cert)
 	return cert, nil
 }
 
+// wantsTokenCert reports whether a TLS request with SNI is made by a CA server
+// for a challenge verification.
+func wantsTokenCert(hello *tls.ClientHelloInfo) bool {
+	// tls-alpn-01
+	if len(hello.SupportedProtos) == 1 && hello.SupportedProtos[0] == acme.ALPNProto {
+		return true
+	}
+	// tls-sni-xx
+	return strings.HasSuffix(hello.ServerName, ".acme.invalid")
+}
+
+func supportsECDSA(hello *tls.ClientHelloInfo) bool {
+	// The "signature_algorithms" extension, if present, limits the key exchange
+	// algorithms allowed by the cipher suites. See RFC 5246, section 7.4.1.4.1.
+	if hello.SignatureSchemes != nil {
+		ecdsaOK := false
+	schemeLoop:
+		for _, scheme := range hello.SignatureSchemes {
+			const tlsECDSAWithSHA1 tls.SignatureScheme = 0x0203 // constant added in Go 1.10
+			switch scheme {
+			case tlsECDSAWithSHA1, tls.ECDSAWithP256AndSHA256,
+				tls.ECDSAWithP384AndSHA384, tls.ECDSAWithP521AndSHA512:
+				ecdsaOK = true
+				break schemeLoop
+			}
+		}
+		if !ecdsaOK {
+			return false
+		}
+	}
+	if hello.SupportedCurves != nil {
+		ecdsaOK := false
+		for _, curve := range hello.SupportedCurves {
+			if curve == tls.CurveP256 {
+				ecdsaOK = true
+				break
+			}
+		}
+		if !ecdsaOK {
+			return false
+		}
+	}
+	for _, suite := range hello.CipherSuites {
+		switch suite {
+		case tls.TLS_ECDHE_ECDSA_WITH_RC4_128_SHA,
+			tls.TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA,
+			tls.TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA,
+			tls.TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256,
+			tls.TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,
+			tls.TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,
+			tls.TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305:
+			return true
+		}
+	}
+	return false
+}
+
 // HTTPHandler configures the Manager to provision ACME "http-01" challenge responses.
 // It returns an http.Handler that responds to the challenges and must be
 // running on port 80. If it receives a request that is not an ACME challenge,
@@ -252,8 +381,8 @@ func (m *Manager) GetCertificate(hello *tls.ClientHelloInfo) (*tls.Certificate,
 // Because the fallback handler is run with unencrypted port 80 requests,
 // the fallback should not serve TLS-only requests.
 //
-// If HTTPHandler is never called, the Manager will only use TLS SNI
-// challenges for domain verification.
+// If HTTPHandler is never called, the Manager will only use the "tls-alpn-01"
+// challenge for domain verification.
 func (m *Manager) HTTPHandler(fallback http.Handler) http.Handler {
 	m.tokensMu.Lock()
 	defer m.tokensMu.Unlock()
@@ -304,16 +433,16 @@ func stripPort(hostport string) string {
 // 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(ctx context.Context, name string) (*tls.Certificate, error) {
+func (m *Manager) cert(ctx context.Context, ck certKey) (*tls.Certificate, error) {
 	m.stateMu.Lock()
-	if s, ok := m.state[name]; ok {
+	if s, ok := m.state[ck]; ok {
 		m.stateMu.Unlock()
 		s.RLock()
 		defer s.RUnlock()
 		return s.tlscert()
 	}
 	defer m.stateMu.Unlock()
-	cert, err := m.cacheGet(ctx, name)
+	cert, err := m.cacheGet(ctx, ck)
 	if err != nil {
 		return nil, err
 	}
@@ -322,25 +451,25 @@ func (m *Manager) cert(ctx context.Context, name string) (*tls.Certificate, erro
 		return nil, errors.New("acme/autocert: private key cannot sign")
 	}
 	if m.state == nil {
-		m.state = make(map[string]*certState)
+		m.state = make(map[certKey]*certState)
 	}
 	s := &certState{
 		key:  signer,
 		cert: cert.Certificate,
 		leaf: cert.Leaf,
 	}
-	m.state[name] = s
-	go m.renew(name, s.key, s.leaf.NotAfter)
+	m.state[ck] = s
+	go m.renew(ck, s.key, s.leaf.NotAfter)
 	return cert, nil
 }
 
 // cacheGet always returns a valid certificate, or an error otherwise.
-// If a cached certficate exists but is not valid, ErrCacheMiss is returned.
-func (m *Manager) cacheGet(ctx context.Context, domain string) (*tls.Certificate, error) {
+// If a cached certificate exists but is not valid, ErrCacheMiss is returned.
+func (m *Manager) cacheGet(ctx context.Context, ck certKey) (*tls.Certificate, error) {
 	if m.Cache == nil {
 		return nil, ErrCacheMiss
 	}
-	data, err := m.Cache.Get(ctx, domain)
+	data, err := m.Cache.Get(ctx, ck.String())
 	if err != nil {
 		return nil, err
 	}
@@ -371,7 +500,7 @@ func (m *Manager) cacheGet(ctx context.Context, domain string) (*tls.Certificate
 	}
 
 	// verify and create TLS cert
-	leaf, err := validCert(domain, pubDER, privKey)
+	leaf, err := validCert(ck, pubDER, privKey, m.now())
 	if err != nil {
 		return nil, ErrCacheMiss
 	}
@@ -383,7 +512,7 @@ func (m *Manager) cacheGet(ctx context.Context, domain string) (*tls.Certificate
 	return tlscert, nil
 }
 
-func (m *Manager) cachePut(ctx context.Context, domain string, tlscert *tls.Certificate) error {
+func (m *Manager) cachePut(ctx context.Context, ck certKey, tlscert *tls.Certificate) error {
 	if m.Cache == nil {
 		return nil
 	}
@@ -415,7 +544,7 @@ func (m *Manager) cachePut(ctx context.Context, domain string, tlscert *tls.Cert
 		}
 	}
 
-	return m.Cache.Put(ctx, domain, buf.Bytes())
+	return m.Cache.Put(ctx, ck.String(), buf.Bytes())
 }
 
 func encodeECDSAKey(w io.Writer, key *ecdsa.PrivateKey) error {
@@ -432,9 +561,9 @@ func encodeECDSAKey(w io.Writer, key *ecdsa.PrivateKey) error {
 //
 // 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) {
+func (m *Manager) createCert(ctx context.Context, ck certKey) (*tls.Certificate, error) {
 	// TODO: maybe rewrite this whole piece using sync.Once
-	state, err := m.certState(domain)
+	state, err := m.certState(ck)
 	if err != nil {
 		return nil, err
 	}
@@ -452,44 +581,44 @@ func (m *Manager) createCert(ctx context.Context, domain string) (*tls.Certifica
 	defer state.Unlock()
 	state.locked = false
 
-	der, leaf, err := m.authorizedCert(ctx, state.key, domain)
+	der, leaf, err := m.authorizedCert(ctx, state.key, ck)
 	if err != nil {
 		// Remove the failed state after some time,
 		// making the manager call createCert again on the following TLS hello.
 		time.AfterFunc(createCertRetryAfter, func() {
-			defer testDidRemoveState(domain)
+			defer testDidRemoveState(ck)
 			m.stateMu.Lock()
 			defer m.stateMu.Unlock()
 			// Verify the state hasn't changed and it's still invalid
 			// before deleting.
-			s, ok := m.state[domain]
+			s, ok := m.state[ck]
 			if !ok {
 				return
 			}
-			if _, err := validCert(domain, s.cert, s.key); err == nil {
+			if _, err := validCert(ck, s.cert, s.key, m.now()); err == nil {
 				return
 			}
-			delete(m.state, domain)
+			delete(m.state, ck)
 		})
 		return nil, err
 	}
 	state.cert = der
 	state.leaf = leaf
-	go m.renew(domain, state.key, state.leaf.NotAfter)
+	go m.renew(ck, 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) {
+func (m *Manager) certState(ck certKey) (*certState, error) {
 	m.stateMu.Lock()
 	defer m.stateMu.Unlock()
 	if m.state == nil {
-		m.state = make(map[string]*certState)
+		m.state = make(map[certKey]*certState)
 	}
 	// existing state
-	if state, ok := m.state[domain]; ok {
+	if state, ok := m.state[ck]; ok {
 		return state, nil
 	}
 
@@ -498,7 +627,7 @@ func (m *Manager) certState(domain string) (*certState, error) {
 		err error
 		key crypto.Signer
 	)
-	if m.ForceRSA {
+	if ck.isRSA {
 		key, err = rsa.GenerateKey(rand.Reader, 2048)
 	} else {
 		key, err = ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
@@ -512,22 +641,22 @@ func (m *Manager) certState(domain string) (*certState, error) {
 		locked: true,
 	}
 	state.Lock() // will be unlocked by m.certState caller
-	m.state[domain] = state
+	m.state[ck] = state
 	return state, nil
 }
 
 // authorizedCert starts the 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) {
+func (m *Manager) authorizedCert(ctx context.Context, key crypto.Signer, ck certKey) (der [][]byte, leaf *x509.Certificate, err error) {
 	client, err := m.acmeClient(ctx)
 	if err != nil {
 		return nil, nil, err
 	}
 
-	if err := m.verify(ctx, client, domain); err != nil {
+	if err := m.verify(ctx, client, ck.domain); err != nil {
 		return nil, nil, err
 	}
-	csr, err := certRequest(key, domain)
+	csr, err := certRequest(key, ck.domain, m.ExtraExtensions)
 	if err != nil {
 		return nil, nil, err
 	}
@@ -535,25 +664,55 @@ func (m *Manager) authorizedCert(ctx context.Context, key crypto.Signer, domain
 	if err != nil {
 		return nil, nil, err
 	}
-	leaf, err = validCert(domain, der, key)
+	leaf, err = validCert(ck, der, key, m.now())
 	if err != nil {
 		return nil, nil, err
 	}
 	return der, leaf, nil
 }
 
+// revokePendingAuthz revokes all authorizations idenfied by the elements of uri slice.
+// It ignores revocation errors.
+func (m *Manager) revokePendingAuthz(ctx context.Context, uri []string) {
+	client, err := m.acmeClient(ctx)
+	if err != nil {
+		return
+	}
+	for _, u := range uri {
+		client.RevokeAuthorization(ctx, u)
+	}
+}
+
 // verify runs the identifier (domain) authorization flow
 // using each applicable ACME challenge type.
 func (m *Manager) verify(ctx context.Context, client *acme.Client, domain string) error {
 	// The list of challenge types we'll try to fulfill
 	// in this specific order.
-	challengeTypes := []string{"tls-sni-02", "tls-sni-01"}
+	challengeTypes := []string{"tls-alpn-01", "tls-sni-02", "tls-sni-01"}
 	m.tokensMu.RLock()
 	if m.tryHTTP01 {
 		challengeTypes = append(challengeTypes, "http-01")
 	}
 	m.tokensMu.RUnlock()
 
+	// Keep track of pending authzs and revoke the ones that did not validate.
+	pendingAuthzs := make(map[string]bool)
+	defer func() {
+		var uri []string
+		for k, pending := range pendingAuthzs {
+			if pending {
+				uri = append(uri, k)
+			}
+		}
+		if len(uri) > 0 {
+			// Use "detached" background context.
+			// The revocations need not happen in the current verification flow.
+			go m.revokePendingAuthz(context.Background(), uri)
+		}
+	}()
+
+	// errs accumulates challenge failure errors, printed if all fail
+	errs := make(map[*acme.Challenge]error)
 	var nextTyp int // challengeType index of the next challenge type to try
 	for {
 		// Start domain authorization and get the challenge.
@@ -570,6 +729,8 @@ func (m *Manager) verify(ctx context.Context, client *acme.Client, domain string
 			return fmt.Errorf("acme/autocert: invalid authorization %q", authz.URI)
 		}
 
+		pendingAuthzs[authz.URI] = true
+
 		// Pick the next preferred challenge.
 		var chal *acme.Challenge
 		for chal == nil && nextTyp < len(challengeTypes) {
@@ -577,28 +738,44 @@ func (m *Manager) verify(ctx context.Context, client *acme.Client, domain string
 			nextTyp++
 		}
 		if chal == nil {
-			return fmt.Errorf("acme/autocert: unable to authorize %q; tried %q", domain, challengeTypes)
+			errorMsg := fmt.Sprintf("acme/autocert: unable to authorize %q", domain)
+			for chal, err := range errs {
+				errorMsg += fmt.Sprintf("; challenge %q failed with error: %v", chal.Type, err)
+			}
+			return errors.New(errorMsg)
 		}
-		cleanup, err := m.fulfill(ctx, client, chal)
+		cleanup, err := m.fulfill(ctx, client, chal, domain)
 		if err != nil {
+			errs[chal] = err
 			continue
 		}
 		defer cleanup()
 		if _, err := client.Accept(ctx, chal); err != nil {
+			errs[chal] = err
 			continue
 		}
 
 		// A challenge is fulfilled and accepted: wait for the CA to validate.
-		if _, err := client.WaitAuthorization(ctx, authz.URI); err == nil {
-			return nil
+		if _, err := client.WaitAuthorization(ctx, authz.URI); err != nil {
+			errs[chal] = err
+			continue
 		}
+		delete(pendingAuthzs, authz.URI)
+		return nil
 	}
 }
 
 // fulfill provisions a response to the challenge chal.
 // The cleanup is non-nil only if provisioning succeeded.
-func (m *Manager) fulfill(ctx context.Context, client *acme.Client, chal *acme.Challenge) (cleanup func(), err error) {
+func (m *Manager) fulfill(ctx context.Context, client *acme.Client, chal *acme.Challenge, domain string) (cleanup func(), err error) {
 	switch chal.Type {
+	case "tls-alpn-01":
+		cert, err := client.TLSALPN01ChallengeCert(chal.Token, domain)
+		if err != nil {
+			return nil, err
+		}
+		m.putCertToken(ctx, domain, &cert)
+		return func() { go m.deleteCertToken(domain) }, nil
 	case "tls-sni-01":
 		cert, name, err := client.TLSSNI01ChallengeCert(chal.Token)
 		if err != nil {
@@ -634,8 +811,8 @@ func pickChallenge(typ string, chal []*acme.Challenge) *acme.Challenge {
 	return nil
 }
 
-// putCertToken stores the cert under the named key in both m.certTokens map
-// and m.Cache.
+// putCertToken stores the token certificate with the specified name
+// in both m.certTokens map and m.Cache.
 func (m *Manager) putCertToken(ctx context.Context, name string, cert *tls.Certificate) {
 	m.tokensMu.Lock()
 	defer m.tokensMu.Unlock()
@@ -643,17 +820,18 @@ func (m *Manager) putCertToken(ctx context.Context, name string, cert *tls.Certi
 		m.certTokens = make(map[string]*tls.Certificate)
 	}
 	m.certTokens[name] = cert
-	m.cachePut(ctx, name, cert)
+	m.cachePut(ctx, certKey{domain: name, isToken: true}, cert)
 }
 
-// deleteCertToken removes the token certificate for the specified domain name
+// deleteCertToken removes the token certificate with the specified name
 // from both m.certTokens map and m.Cache.
 func (m *Manager) deleteCertToken(name string) {
 	m.tokensMu.Lock()
 	defer m.tokensMu.Unlock()
 	delete(m.certTokens, name)
 	if m.Cache != nil {
-		m.Cache.Delete(context.Background(), name)
+		ck := certKey{domain: name, isToken: true}
+		m.Cache.Delete(context.Background(), ck.String())
 	}
 }
 
@@ -704,7 +882,7 @@ func (m *Manager) deleteHTTPToken(tokenPath string) {
 // httpTokenCacheKey returns a key at which an http-01 token value may be stored
 // in the Manager's optional Cache.
 func httpTokenCacheKey(tokenPath string) string {
-	return "http-01-" + path.Base(tokenPath)
+	return path.Base(tokenPath) + "+http-01"
 }
 
 // renew starts a cert renewal timer loop, one per domain.
@@ -715,18 +893,18 @@ func httpTokenCacheKey(tokenPath string) string {
 //
 // 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) {
+func (m *Manager) renew(ck certKey, key crypto.Signer, exp time.Time) {
 	m.renewalMu.Lock()
 	defer m.renewalMu.Unlock()
-	if m.renewal[domain] != nil {
+	if m.renewal[ck] != nil {
 		// another goroutine is already on it
 		return
 	}
 	if m.renewal == nil {
-		m.renewal = make(map[string]*domainRenewal)
+		m.renewal = make(map[certKey]*domainRenewal)
 	}
-	dr := &domainRenewal{m: m, domain: domain, key: key}
-	m.renewal[domain] = dr
+	dr := &domainRenewal{m: m, ck: ck, key: key}
+	m.renewal[ck] = dr
 	dr.start(exp)
 }
 
@@ -742,7 +920,10 @@ func (m *Manager) stopRenew() {
 }
 
 func (m *Manager) accountKey(ctx context.Context) (crypto.Signer, error) {
-	const keyName = "acme_account.key"
+	const keyName = "acme_account+key"
+
+	// Previous versions of autocert stored the value under a different key.
+	const legacyKeyName = "acme_account.key"
 
 	genKey := func() (*ecdsa.PrivateKey, error) {
 		return ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
@@ -753,6 +934,9 @@ func (m *Manager) accountKey(ctx context.Context) (crypto.Signer, error) {
 	}
 
 	data, err := m.Cache.Get(ctx, keyName)
+	if err == ErrCacheMiss {
+		data, err = m.Cache.Get(ctx, legacyKeyName)
+	}
 	if err == ErrCacheMiss {
 		key, err := genKey()
 		if err != nil {
@@ -824,6 +1008,13 @@ func (m *Manager) renewBefore() time.Duration {
 	return 720 * time.Hour // 30 days
 }
 
+func (m *Manager) now() time.Time {
+	if m.nowFunc != nil {
+		return m.nowFunc()
+	}
+	return time.Now()
+}
+
 // certState is ready when its mutex is unlocked for reading.
 type certState struct {
 	sync.RWMutex
@@ -849,12 +1040,12 @@ func (s *certState) tlscert() (*tls.Certificate, error) {
 	}, 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) {
+// certRequest generates a CSR for the given common name cn and optional SANs.
+func certRequest(key crypto.Signer, cn string, ext []pkix.Extension, san ...string) ([]byte, error) {
 	req := &x509.CertificateRequest{
-		Subject:  pkix.Name{CommonName: cn},
-		DNSNames: san,
+		Subject:         pkix.Name{CommonName: cn},
+		DNSNames:        san,
+		ExtraExtensions: ext,
 	}
 	return x509.CreateCertificateRequest(rand.Reader, req, key)
 }
@@ -885,12 +1076,12 @@ func parsePrivateKey(der []byte) (crypto.Signer, error) {
 	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.
+// validCert parses a cert chain provided as der argument and verifies the leaf and der[0]
+// correspond to the private key, the domain and key type match, and expiration dates
+// are valid. 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) {
+func validCert(ck certKey, der [][]byte, key crypto.Signer, now time.Time) (leaf *x509.Certificate, err error) {
 	// parse public part(s)
 	var n int
 	for _, b := range der {
@@ -902,22 +1093,21 @@ func validCert(domain string, der [][]byte, key crypto.Signer) (leaf *x509.Certi
 		n += copy(pub[n:], b)
 	}
 	x509Cert, err := x509.ParseCertificates(pub)
-	if len(x509Cert) == 0 {
+	if err != nil || 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 {
+	if err := leaf.VerifyHostname(ck.domain); err != nil {
 		return nil, err
 	}
-	// ensure the leaf corresponds to the private key
+	// ensure the leaf corresponds to the private key and matches the certKey type
 	switch pub := leaf.PublicKey.(type) {
 	case *rsa.PublicKey:
 		prv, ok := key.(*rsa.PrivateKey)
@@ -927,6 +1117,9 @@ func validCert(domain string, der [][]byte, key crypto.Signer) (leaf *x509.Certi
 		if pub.N.Cmp(prv.N) != 0 {
 			return nil, errors.New("acme/autocert: private key does not match public key")
 		}
+		if !ck.isRSA && !ck.isToken {
+			return nil, errors.New("acme/autocert: key type does not match expected value")
+		}
 	case *ecdsa.PublicKey:
 		prv, ok := key.(*ecdsa.PrivateKey)
 		if !ok {
@@ -935,6 +1128,9 @@ func validCert(domain string, der [][]byte, key crypto.Signer) (leaf *x509.Certi
 		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")
 		}
+		if ck.isRSA && !ck.isToken {
+			return nil, errors.New("acme/autocert: key type does not match expected value")
+		}
 	default:
 		return nil, errors.New("acme/autocert: unknown public key algorithm")
 	}
@@ -955,8 +1151,6 @@ func (r *lockedMathRand) int63n(max int64) int64 {
 
 // For easier testing.
 var (
-	timeNow = time.Now
-
 	// Called when a state is removed.
-	testDidRemoveState = func(domain string) {}
+	testDidRemoveState = func(certKey) {}
 )
diff --git a/vendor/golang.org/x/crypto/acme/autocert/cache.go b/vendor/golang.org/x/crypto/acme/autocert/cache.go
index 61a5fd239a..aa9aa845c8 100644
--- a/vendor/golang.org/x/crypto/acme/autocert/cache.go
+++ b/vendor/golang.org/x/crypto/acme/autocert/cache.go
@@ -16,10 +16,10 @@ import (
 var ErrCacheMiss = errors.New("acme/autocert: certificate cache miss")
 
 // Cache is used by Manager to store and retrieve previously obtained certificates
-// as opaque data.
+// and other account data as opaque blobs.
 //
-// The key argument of the methods refers to a domain name but need not be an FQDN.
-// Cache implementations should not rely on the key naming pattern.
+// Cache implementations should not rely on the key naming pattern. Keys can
+// include any printable ASCII characters, except the following: \/:*?"<>|
 type Cache interface {
 	// Get returns a certificate data for the specified key.
 	// If there's no such key, Get returns ErrCacheMiss.
diff --git a/vendor/golang.org/x/crypto/acme/autocert/listener.go b/vendor/golang.org/x/crypto/acme/autocert/listener.go
index d744df0ed0..1e069818a5 100644
--- a/vendor/golang.org/x/crypto/acme/autocert/listener.go
+++ b/vendor/golang.org/x/crypto/acme/autocert/listener.go
@@ -72,11 +72,8 @@ func NewListener(domains ...string) net.Listener {
 // the Manager m's Prompt, Cache, HostPolicy, and other desired options.
 func (m *Manager) Listener() net.Listener {
 	ln := &listener{
-		m: m,
-		conf: &tls.Config{
-			GetCertificate: m.GetCertificate,           // bonus: panic on nil m
-			NextProtos:     []string{"h2", "http/1.1"}, // Enable HTTP/2
-		},
+		m:    m,
+		conf: m.TLSConfig(),
 	}
 	ln.tcpListener, ln.tcpListenErr = net.Listen("tcp", ":443")
 	return ln
diff --git a/vendor/golang.org/x/crypto/acme/autocert/renewal.go b/vendor/golang.org/x/crypto/acme/autocert/renewal.go
index 3fa4d61a22..665f870dcd 100644
--- a/vendor/golang.org/x/crypto/acme/autocert/renewal.go
+++ b/vendor/golang.org/x/crypto/acme/autocert/renewal.go
@@ -17,9 +17,9 @@ const renewJitter = time.Hour
 // domainRenewal tracks the state used by the periodic timers
 // renewing a single domain's cert.
 type domainRenewal struct {
-	m      *Manager
-	domain string
-	key    crypto.Signer
+	m   *Manager
+	ck  certKey
+	key crypto.Signer
 
 	timerMu sync.Mutex
 	timer   *time.Timer
@@ -77,7 +77,7 @@ func (dr *domainRenewal) updateState(state *certState) {
 	dr.m.stateMu.Lock()
 	defer dr.m.stateMu.Unlock()
 	dr.key = state.key
-	dr.m.state[dr.domain] = state
+	dr.m.state[dr.ck] = state
 }
 
 // do is similar to Manager.createCert but it doesn't lock a Manager.state item.
@@ -91,7 +91,7 @@ func (dr *domainRenewal) updateState(state *certState) {
 func (dr *domainRenewal) do(ctx context.Context) (time.Duration, error) {
 	// a race is likely unavoidable in a distributed environment
 	// but we try nonetheless
-	if tlscert, err := dr.m.cacheGet(ctx, dr.domain); err == nil {
+	if tlscert, err := dr.m.cacheGet(ctx, dr.ck); err == nil {
 		next := dr.next(tlscert.Leaf.NotAfter)
 		if next > dr.m.renewBefore()+renewJitter {
 			signer, ok := tlscert.PrivateKey.(crypto.Signer)
@@ -107,7 +107,7 @@ func (dr *domainRenewal) do(ctx context.Context) (time.Duration, error) {
 		}
 	}
 
-	der, leaf, err := dr.m.authorizedCert(ctx, dr.key, dr.domain)
+	der, leaf, err := dr.m.authorizedCert(ctx, dr.key, dr.ck)
 	if err != nil {
 		return 0, err
 	}
@@ -120,7 +120,7 @@ func (dr *domainRenewal) do(ctx context.Context) (time.Duration, error) {
 	if err != nil {
 		return 0, err
 	}
-	if err := dr.m.cachePut(ctx, dr.domain, tlscert); err != nil {
+	if err := dr.m.cachePut(ctx, dr.ck, tlscert); err != nil {
 		return 0, err
 	}
 	dr.updateState(state)
@@ -128,7 +128,7 @@ func (dr *domainRenewal) do(ctx context.Context) (time.Duration, error) {
 }
 
 func (dr *domainRenewal) next(expiry time.Time) time.Duration {
-	d := expiry.Sub(timeNow()) - dr.m.renewBefore()
+	d := expiry.Sub(dr.m.now()) - dr.m.renewBefore()
 	// add a bit of randomness to renew deadline
 	n := pseudoRand.int63n(int64(renewJitter))
 	d -= time.Duration(n)
diff --git a/vendor/golang.org/x/crypto/acme/http.go b/vendor/golang.org/x/crypto/acme/http.go
new file mode 100644
index 0000000000..a43ce6a5fe
--- /dev/null
+++ b/vendor/golang.org/x/crypto/acme/http.go
@@ -0,0 +1,281 @@
+// Copyright 2018 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
+
+import (
+	"bytes"
+	"context"
+	"crypto"
+	"crypto/rand"
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"math/big"
+	"net/http"
+	"strconv"
+	"strings"
+	"time"
+)
+
+// retryTimer encapsulates common logic for retrying unsuccessful requests.
+// It is not safe for concurrent use.
+type retryTimer struct {
+	// backoffFn provides backoff delay sequence for retries.
+	// See Client.RetryBackoff doc comment.
+	backoffFn func(n int, r *http.Request, res *http.Response) time.Duration
+	// n is the current retry attempt.
+	n int
+}
+
+func (t *retryTimer) inc() {
+	t.n++
+}
+
+// backoff pauses the current goroutine as described in Client.RetryBackoff.
+func (t *retryTimer) backoff(ctx context.Context, r *http.Request, res *http.Response) error {
+	d := t.backoffFn(t.n, r, res)
+	if d <= 0 {
+		return fmt.Errorf("acme: no more retries for %s; tried %d time(s)", r.URL, t.n)
+	}
+	wakeup := time.NewTimer(d)
+	defer wakeup.Stop()
+	select {
+	case <-ctx.Done():
+		return ctx.Err()
+	case <-wakeup.C:
+		return nil
+	}
+}
+
+func (c *Client) retryTimer() *retryTimer {
+	f := c.RetryBackoff
+	if f == nil {
+		f = defaultBackoff
+	}
+	return &retryTimer{backoffFn: f}
+}
+
+// defaultBackoff provides default Client.RetryBackoff implementation
+// using a truncated exponential backoff algorithm,
+// as described in Client.RetryBackoff.
+//
+// The n argument is always bounded between 1 and 30.
+// The returned value is always greater than 0.
+func defaultBackoff(n int, r *http.Request, res *http.Response) time.Duration {
+	const max = 10 * time.Second
+	var jitter time.Duration
+	if x, err := rand.Int(rand.Reader, big.NewInt(1000)); err == nil {
+		// Set the minimum to 1ms to avoid a case where
+		// an invalid Retry-After value is parsed into 0 below,
+		// resulting in the 0 returned value which would unintentionally
+		// stop the retries.
+		jitter = (1 + time.Duration(x.Int64())) * time.Millisecond
+	}
+	if v, ok := res.Header["Retry-After"]; ok {
+		return retryAfter(v[0]) + jitter
+	}
+
+	if n < 1 {
+		n = 1
+	}
+	if n > 30 {
+		n = 30
+	}
+	d := time.Duration(1<<uint(n-1))*time.Second + jitter
+	if d > max {
+		return max
+	}
+	return d
+}
+
+// retryAfter parses a Retry-After HTTP header value,
+// trying to convert v into an int (seconds) or use http.ParseTime otherwise.
+// It returns zero value if v cannot be parsed.
+func retryAfter(v string) time.Duration {
+	if i, err := strconv.Atoi(v); err == nil {
+		return time.Duration(i) * time.Second
+	}
+	t, err := http.ParseTime(v)
+	if err != nil {
+		return 0
+	}
+	return t.Sub(timeNow())
+}
+
+// resOkay is a function that reports whether the provided response is okay.
+// It is expected to keep the response body unread.
+type resOkay func(*http.Response) bool
+
+// wantStatus returns a function which reports whether the code
+// matches the status code of a response.
+func wantStatus(codes ...int) resOkay {
+	return func(res *http.Response) bool {
+		for _, code := range codes {
+			if code == res.StatusCode {
+				return true
+			}
+		}
+		return false
+	}
+}
+
+// get issues an unsigned GET request to the specified URL.
+// It returns a non-error value only when ok reports true.
+//
+// get retries unsuccessful attempts according to c.RetryBackoff
+// until the context is done or a non-retriable error is received.
+func (c *Client) get(ctx context.Context, url string, ok resOkay) (*http.Response, error) {
+	retry := c.retryTimer()
+	for {
+		req, err := http.NewRequest("GET", url, nil)
+		if err != nil {
+			return nil, err
+		}
+		res, err := c.doNoRetry(ctx, req)
+		switch {
+		case err != nil:
+			return nil, err
+		case ok(res):
+			return res, nil
+		case isRetriable(res.StatusCode):
+			retry.inc()
+			resErr := responseError(res)
+			res.Body.Close()
+			// Ignore the error value from retry.backoff
+			// and return the one from last retry, as received from the CA.
+			if retry.backoff(ctx, req, res) != nil {
+				return nil, resErr
+			}
+		default:
+			defer res.Body.Close()
+			return nil, responseError(res)
+		}
+	}
+}
+
+// post issues a signed POST request in JWS format using the provided key
+// to the specified URL.
+// It returns a non-error value only when ok reports true.
+//
+// post retries unsuccessful attempts according to c.RetryBackoff
+// until the context is done or a non-retriable error is received.
+// It uses postNoRetry to make individual requests.
+func (c *Client) post(ctx context.Context, key crypto.Signer, url string, body interface{}, ok resOkay) (*http.Response, error) {
+	retry := c.retryTimer()
+	for {
+		res, req, err := c.postNoRetry(ctx, key, url, body)
+		if err != nil {
+			return nil, err
+		}
+		if ok(res) {
+			return res, nil
+		}
+		resErr := responseError(res)
+		res.Body.Close()
+		switch {
+		// Check for bad nonce before isRetriable because it may have been returned
+		// with an unretriable response code such as 400 Bad Request.
+		case isBadNonce(resErr):
+			// Consider any previously stored nonce values to be invalid.
+			c.clearNonces()
+		case !isRetriable(res.StatusCode):
+			return nil, resErr
+		}
+		retry.inc()
+		// Ignore the error value from retry.backoff
+		// and return the one from last retry, as received from the CA.
+		if err := retry.backoff(ctx, req, res); err != nil {
+			return nil, resErr
+		}
+	}
+}
+
+// postNoRetry signs the body with the given key and POSTs it to the provided url.
+// The body argument must be JSON-serializable.
+// It is used by c.post to retry unsuccessful attempts.
+func (c *Client) postNoRetry(ctx context.Context, key crypto.Signer, url string, body interface{}) (*http.Response, *http.Request, error) {
+	nonce, err := c.popNonce(ctx, url)
+	if err != nil {
+		return nil, nil, err
+	}
+	b, err := jwsEncodeJSON(body, key, nonce)
+	if err != nil {
+		return nil, nil, err
+	}
+	req, err := http.NewRequest("POST", url, bytes.NewReader(b))
+	if err != nil {
+		return nil, nil, err
+	}
+	req.Header.Set("Content-Type", "application/jose+json")
+	res, err := c.doNoRetry(ctx, req)
+	if err != nil {
+		return nil, nil, err
+	}
+	c.addNonce(res.Header)
+	return res, req, nil
+}
+
+// doNoRetry issues a request req, replacing its context (if any) with ctx.
+func (c *Client) doNoRetry(ctx context.Context, req *http.Request) (*http.Response, error) {
+	res, err := c.httpClient().Do(req.WithContext(ctx))
+	if err != nil {
+		select {
+		case <-ctx.Done():
+			// Prefer the unadorned context error.
+			// (The acme package had tests assuming this, previously from ctxhttp's
+			// behavior, predating net/http supporting contexts natively)
+			// TODO(bradfitz): reconsider this in the future. But for now this
+			// requires no test updates.
+			return nil, ctx.Err()
+		default:
+			return nil, err
+		}
+	}
+	return res, nil
+}
+
+func (c *Client) httpClient() *http.Client {
+	if c.HTTPClient != nil {
+		return c.HTTPClient
+	}
+	return http.DefaultClient
+}
+
+// isBadNonce reports whether err is an ACME "badnonce" error.
+func isBadNonce(err error) bool {
+	// According to the spec badNonce is urn:ietf:params:acme:error:badNonce.
+	// However, ACME servers in the wild return their versions of the error.
+	// See https://tools.ietf.org/html/draft-ietf-acme-acme-02#section-5.4
+	// and https://github.com/letsencrypt/boulder/blob/0e07eacb/docs/acme-divergences.md#section-66.
+	ae, ok := err.(*Error)
+	return ok && strings.HasSuffix(strings.ToLower(ae.ProblemType), ":badnonce")
+}
+
+// isRetriable reports whether a request can be retried
+// based on the response status code.
+//
+// Note that a "bad nonce" error is returned with a non-retriable 400 Bad Request code.
+// Callers should parse the response and check with isBadNonce.
+func isRetriable(code int) bool {
+	return code <= 399 || code >= 500 || code == http.StatusTooManyRequests
+}
+
+// responseError creates an error of Error type from resp.
+func responseError(resp *http.Response) error {
+	// don't care if ReadAll returns an error:
+	// json.Unmarshal will fail in that case anyway
+	b, _ := ioutil.ReadAll(resp.Body)
+	e := &wireError{Status: resp.StatusCode}
+	if err := json.Unmarshal(b, e); err != nil {
+		// this is not a regular error response:
+		// populate detail with anything we received,
+		// e.Status will already contain HTTP response code value
+		e.Detail = string(b)
+		if e.Detail == "" {
+			e.Detail = resp.Status
+		}
+	}
+	return e.error(resp.Header)
+}
diff --git a/vendor/golang.org/x/crypto/acme/jws.go b/vendor/golang.org/x/crypto/acme/jws.go
index 6cbca25de9..1093b50390 100644
--- a/vendor/golang.org/x/crypto/acme/jws.go
+++ b/vendor/golang.org/x/crypto/acme/jws.go
@@ -25,7 +25,7 @@ func jwsEncodeJSON(claimset interface{}, key crypto.Signer, nonce string) ([]byt
 	if err != nil {
 		return nil, err
 	}
-	alg, sha := jwsHasher(key)
+	alg, sha := jwsHasher(key.Public())
 	if alg == "" || !sha.Available() {
 		return nil, ErrUnsupportedKey
 	}
@@ -97,13 +97,16 @@ func jwkEncode(pub crypto.PublicKey) (string, error) {
 }
 
 // jwsSign signs the digest using the given key.
-// It returns ErrUnsupportedKey if the key type is unknown.
-// The hash is used only for RSA keys.
+// 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) {
-	switch key := key.(type) {
-	case *rsa.PrivateKey:
-		return key.Sign(rand.Reader, digest, hash)
-	case *ecdsa.PrivateKey:
+	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
@@ -118,18 +121,18 @@ func jwsSign(key crypto.Signer, hash crypto.Hash, digest []byte) ([]byte, error)
 		copy(sig[size*2-len(sb):], sb)
 		return sig, nil
 	}
-	return nil, ErrUnsupportedKey
+	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(key crypto.Signer) (string, crypto.Hash) {
-	switch key := key.(type) {
-	case *rsa.PrivateKey:
+func jwsHasher(pub crypto.PublicKey) (string, crypto.Hash) {
+	switch pub := pub.(type) {
+	case *rsa.PublicKey:
 		return "RS256", crypto.SHA256
-	case *ecdsa.PrivateKey:
-		switch key.Params().Name {
+	case *ecdsa.PublicKey:
+		switch pub.Params().Name {
 		case "P-256":
 			return "ES256", crypto.SHA256
 		case "P-384":
diff --git a/vendor/golang.org/x/crypto/acme/types.go b/vendor/golang.org/x/crypto/acme/types.go
index 3e199749ec..54792c0650 100644
--- a/vendor/golang.org/x/crypto/acme/types.go
+++ b/vendor/golang.org/x/crypto/acme/types.go
@@ -104,7 +104,7 @@ func RateLimit(err error) (time.Duration, bool) {
 	if e.Header == nil {
 		return 0, true
 	}
-	return retryAfter(e.Header.Get("Retry-After"), 0), true
+	return retryAfter(e.Header.Get("Retry-After")), true
 }
 
 // Account is a user account. It is associated with a private key.
@@ -296,8 +296,8 @@ func (e *wireError) error(h http.Header) *Error {
 	}
 }
 
-// CertOption is an optional argument type for the TLSSNIxChallengeCert methods for
-// customizing a temporary certificate for TLS-SNI challenges.
+// CertOption is an optional argument type for the TLS ChallengeCert methods for
+// customizing a temporary certificate for TLS-based challenges.
 type CertOption interface {
 	privateCertOpt()
 }
@@ -317,7 +317,7 @@ 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,
+// In TLS ChallengeCert 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 {