diff --git a/acme/internal/acmeprobe/prober.go b/acme/internal/acmeprobe/prober.go
new file mode 100644
index 0000000..68c52f2
--- /dev/null
+++ b/acme/internal/acmeprobe/prober.go
@@ -0,0 +1,477 @@
+// Copyright 2019 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.
+
+// The acmeprober program runs against an actual ACME CA implementation.
+// It spins up an HTTP server to fulfill authorization challenges
+// or execute a DNS script to provision a response to dns-01 challenge.
+//
+// For http-01 and tls-alpn-01 challenge types this requires the ACME CA
+// to be able to reach the HTTP server.
+//
+// A usage example:
+//
+//     go run prober.go \
+//       -d https://acme-staging-v02.api.letsencrypt.org/directory \
+//       -f order \
+//       -t http-01 \
+//       -a :8080 \
+//       -domain some.example.org
+//
+// The above assumes a TCP tunnel from some.example.org:80 to 0.0.0.0:8080
+// in order for the test to be able to fulfill http-01 challenge.
+// To test tls-alpn-01 challenge, 443 port would need to be tunneled
+// to 0.0.0.0:8080.
+// When running with dns-01 challenge type, use -s argument instead of -a.
+package main
+
+import (
+	"context"
+	"crypto"
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"crypto/rand"
+	"crypto/tls"
+	"crypto/x509"
+	"encoding/pem"
+	"errors"
+	"flag"
+	"fmt"
+	"log"
+	"net"
+	"net/http"
+	"os"
+	"os/exec"
+	"strings"
+	"time"
+
+	"golang.org/x/crypto/acme"
+)
+
+var (
+	// ACME CA directory URL.
+	// Let's Encrypt v1 prod: https://acme-v01.api.letsencrypt.org/directory
+	// Let's Encrypt v2 prod: https://acme-v02.api.letsencrypt.org/directory
+	// Let's Encrypt v2 staging: https://acme-staging-v02.api.letsencrypt.org/directory
+	// See the following for more CAs implementing ACME protocol:
+	// https://en.wikipedia.org/wiki/Automated_Certificate_Management_Environment#CAs_&_PKIs_that_offer_ACME_certificates
+	directory = flag.String("d", "", "ACME directory URL.")
+	reginfo   = flag.String("r", "", "ACME account registration info.")
+	flow      = flag.String("f", "", "Flow to run: order, preauthz (RFC8555) or preauthz02 (draft-02).")
+	chaltyp   = flag.String("t", "", "Challenge type: tls-alpn-01, http-01 or dns-01.")
+	addr      = flag.String("a", "", "Local server address for tls-alpn-01 and http-01.")
+	dnsscript = flag.String("s", "", "Script to run for provisioning dns-01 challenges.")
+	domain    = flag.String("domain", "", "Space separate domain identifiers.")
+	ipaddr    = flag.String("ip", "", "Space separate IP address identifiers.")
+)
+
+func main() {
+	flag.Usage = func() {
+		fmt.Fprintln(flag.CommandLine.Output(), `
+The prober program runs against an actual ACME CA implementation.
+It spins up an HTTP server to fulfill authorization challenges
+or execute a DNS script to provision a response to dns-01 challenge.
+
+For http-01 and tls-alpn-01 challenge types this requires the ACME CA
+to be able to reach the HTTP server.
+
+A usage example:
+
+    go run prober.go \
+      -d https://acme-staging-v02.api.letsencrypt.org/directory \
+      -f order \
+      -t http-01 \
+      -a :8080 \
+      -domain some.example.org
+
+The above assumes a TCP tunnel from some.example.org:80 to 0.0.0.0:8080
+in order for the test to be able to fulfill http-01 challenge.
+To test tls-alpn-01 challenge, 443 port would need to be tunneled
+to 0.0.0.0:8080.
+When running with dns-01 challenge type, use -s argument instead of -a.
+		`)
+		flag.PrintDefaults()
+	}
+	flag.Parse()
+
+	identifiers := acme.DomainIDs(strings.Fields(*domain)...)
+	identifiers = append(identifiers, acme.IPIDs(strings.Fields(*ipaddr)...)...)
+	if len(identifiers) == 0 {
+		log.Fatal("at least one domain or IP addr identifier is required")
+	}
+
+	// Duration of the whole run.
+	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Minute)
+	defer cancel()
+
+	// Create and register a new account.
+	akey, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
+	if err != nil {
+		log.Fatal(err)
+	}
+	cl := &acme.Client{Key: akey, DirectoryURL: *directory}
+	a := &acme.Account{Contact: strings.Fields(*reginfo)}
+	if _, err := cl.Register(ctx, a, acme.AcceptTOS); err != nil {
+		log.Fatalf("Register: %v", err)
+	}
+
+	// Run the desired flow test.
+	p := &prober{
+		client:    cl,
+		chalType:  *chaltyp,
+		localAddr: *addr,
+		dnsScript: *dnsscript,
+	}
+	switch *flow {
+	case "order":
+		p.runOrder(ctx, identifiers)
+	case "preauthz":
+		p.runPreauthz(ctx, identifiers)
+	case "preauthz02":
+		p.runPreauthzLegacy(ctx, identifiers)
+	default:
+		log.Fatalf("unknown flow: %q", *flow)
+	}
+	if len(p.errors) > 0 {
+		os.Exit(1)
+	}
+}
+
+type prober struct {
+	client    *acme.Client
+	chalType  string
+	localAddr string
+	dnsScript string
+
+	errors []error
+}
+
+func (p *prober) errorf(format string, a ...interface{}) {
+	err := fmt.Errorf(format, a...)
+	log.Print(err)
+	p.errors = append(p.errors, err)
+}
+
+func (p *prober) runOrder(ctx context.Context, identifiers []acme.AuthzID) {
+	// Create a new order and pick a challenge.
+	// Note that Let's Encrypt will reply with 400 error:malformed
+	// "NotBefore and NotAfter are not supported" when providing a NotAfter
+	// value like WithOrderNotAfter(time.Now().Add(24 * time.Hour)).
+	o, err := p.client.AuthorizeOrder(ctx, identifiers)
+	if err != nil {
+		log.Fatalf("AuthorizeOrder: %v", err)
+	}
+
+	var zurls []string
+	for _, u := range o.AuthzURLs {
+		z, err := p.client.GetAuthorization(ctx, u)
+		if err != nil {
+			log.Fatalf("GetAuthorization(%q): %v", u, err)
+		}
+		log.Printf("%+v", z)
+		if z.Status != acme.StatusPending {
+			log.Printf("authz status is %q; skipping", z.Status)
+			continue
+		}
+		if err := p.fulfill(ctx, z); err != nil {
+			log.Fatalf("fulfill(%s): %v", z.URI, err)
+		}
+		zurls = append(zurls, z.URI)
+		log.Printf("authorized for %+v", z.Identifier)
+	}
+
+	log.Print("all challenges are done")
+	if _, err := p.client.WaitOrder(ctx, o.URI); err != nil {
+		log.Fatalf("WaitOrder(%q): %v", o.URI, err)
+	}
+	csr, certkey := newCSR(identifiers)
+	der, curl, err := p.client.CreateOrderCert(ctx, o.FinalizeURL, csr, true)
+	if err != nil {
+		log.Fatalf("CreateOrderCert: %v", err)
+	}
+	log.Printf("cert URL: %s", curl)
+	if err := checkCert(der, identifiers); err != nil {
+		p.errorf("invalid cert: %v", err)
+	}
+
+	// Deactivate all authorizations we satisfied earlier.
+	for _, v := range zurls {
+		if err := p.client.RevokeAuthorization(ctx, v); err != nil {
+			p.errorf("RevokAuthorization(%q): %v", v, err)
+			continue
+		}
+	}
+	// Deactivate the account. We don't need it for any further calls.
+	if err := p.client.DeactivateReg(ctx); err != nil {
+		p.errorf("DeactivateReg: %v", err)
+	}
+	// Try revoking the issued cert using its private key.
+	if err := p.client.RevokeCert(ctx, certkey, der[0], acme.CRLReasonCessationOfOperation); err != nil {
+		p.errorf("RevokeCert: %v", err)
+	}
+}
+
+func (p *prober) runPreauthz(ctx context.Context, identifiers []acme.AuthzID) {
+	dir, err := p.client.Discover(ctx)
+	if dir.AuthzURL == "" {
+		log.Fatal("CA does not support pre-authorization")
+	}
+
+	var zurls []string
+	for _, id := range identifiers {
+		z, err := authorize(ctx, p.client, id)
+		if err != nil {
+			log.Fatalf("AuthorizeID(%+v): %v", z, err)
+		}
+		if z.Status == acme.StatusValid {
+			log.Printf("authz %s is valid; skipping", z.URI)
+			continue
+		}
+		if err := p.fulfill(ctx, z); err != nil {
+			log.Fatalf("fulfill(%s): %v", z.URI, err)
+		}
+		zurls = append(zurls, z.URI)
+		log.Printf("authorized for %+v", id)
+	}
+
+	// We should be all set now.
+	// Expect all authorizations to be satisfied.
+	log.Print("all challenges are done")
+	o, err := p.client.AuthorizeOrder(ctx, identifiers)
+	if err != nil {
+		log.Fatalf("AuthorizeOrder: %v", err)
+	}
+	waitCtx, cancel := context.WithTimeout(ctx, time.Minute)
+	defer cancel()
+	if _, err := p.client.WaitOrder(waitCtx, o.URI); err != nil {
+		log.Fatalf("WaitOrder(%q): %v", o.URI, err)
+	}
+	csr, certkey := newCSR(identifiers)
+	der, curl, err := p.client.CreateOrderCert(ctx, o.FinalizeURL, csr, true)
+	if err != nil {
+		log.Fatalf("CreateOrderCert: %v", err)
+	}
+	log.Printf("cert URL: %s", curl)
+	if err := checkCert(der, identifiers); err != nil {
+		p.errorf("invalid cert: %v", err)
+	}
+
+	// Deactivate all authorizations we satisfied earlier.
+	for _, v := range zurls {
+		if err := p.client.RevokeAuthorization(ctx, v); err != nil {
+			p.errorf("RevokeAuthorization(%q): %v", v, err)
+			continue
+		}
+	}
+	// Deactivate the account. We don't need it for any further calls.
+	if err := p.client.DeactivateReg(ctx); err != nil {
+		p.errorf("DeactivateReg: %v", err)
+	}
+	// Try revoking the issued cert using its private key.
+	if err := p.client.RevokeCert(ctx, certkey, der[0], acme.CRLReasonCessationOfOperation); err != nil {
+		p.errorf("RevokeCert: %v", err)
+	}
+}
+
+func (p *prober) runPreauthzLegacy(ctx context.Context, identifiers []acme.AuthzID) {
+	var zurls []string
+	for _, id := range identifiers {
+		z, err := authorize(ctx, p.client, id)
+		if err != nil {
+			log.Fatalf("AuthorizeID(%+v): %v", id, err)
+		}
+		if z.Status == acme.StatusValid {
+			log.Printf("authz %s is valid; skipping", z.URI)
+			continue
+		}
+		if err := p.fulfill(ctx, z); err != nil {
+			log.Fatalf("fulfill(%s): %v", z.URI, err)
+		}
+		zurls = append(zurls, z.URI)
+		log.Printf("authorized for %+v", id)
+	}
+
+	// We should be all set now.
+	log.Print("all authorizations are done")
+	csr, certkey := newCSR(identifiers)
+	der, curl, err := p.client.CreateCert(ctx, csr, 48*time.Hour, true)
+	if err != nil {
+		log.Fatalf("CreateCert: %v", err)
+	}
+	log.Printf("cert URL: %s", curl)
+	if err := checkCert(der, identifiers); err != nil {
+		p.errorf("invalid cert: %v", err)
+	}
+
+	// Deactivate all authorizations we satisfied earlier.
+	for _, v := range zurls {
+		if err := p.client.RevokeAuthorization(ctx, v); err != nil {
+			p.errorf("RevokAuthorization(%q): %v", v, err)
+			continue
+		}
+	}
+	// Try revoking the issued cert using its private key.
+	if err := p.client.RevokeCert(ctx, certkey, der[0], acme.CRLReasonCessationOfOperation); err != nil {
+		p.errorf("RevokeCert: %v", err)
+	}
+
+}
+
+func (p *prober) fulfill(ctx context.Context, z *acme.Authorization) error {
+	var chal *acme.Challenge
+	for i, c := range z.Challenges {
+		log.Printf("challenge %d: %+v", i, c)
+		if c.Type == p.chalType {
+			log.Printf("picked %s for authz %s", c.URI, z.URI)
+			chal = c
+		}
+	}
+	if chal == nil {
+		return fmt.Errorf("challenge type %q wasn't offered for authz %s", p.chalType, z.URI)
+	}
+
+	switch chal.Type {
+	case "tls-alpn-01":
+		return p.runTLSALPN01(ctx, z, chal)
+	case "http-01":
+		return p.runHTTP01(ctx, z, chal)
+	case "dns-01":
+		return p.runDNS01(ctx, z, chal)
+	default:
+		return fmt.Errorf("unknown challenge type %q", chal.Type)
+	}
+}
+
+func (p *prober) runTLSALPN01(ctx context.Context, z *acme.Authorization, chal *acme.Challenge) error {
+	tokenCert, err := p.client.TLSALPN01ChallengeCert(chal.Token, z.Identifier.Value)
+	if err != nil {
+		return fmt.Errorf("TLSALPN01ChallengeCert: %v", err)
+	}
+	s := &http.Server{
+		Addr: p.localAddr,
+		TLSConfig: &tls.Config{
+			NextProtos: []string{acme.ALPNProto},
+			GetCertificate: func(hello *tls.ClientHelloInfo) (*tls.Certificate, error) {
+				log.Printf("hello: %+v", hello)
+				return &tokenCert, nil
+			},
+		},
+		Handler: http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			log.Printf("%s %s", r.Method, r.URL)
+			w.WriteHeader(http.StatusNotFound)
+		}),
+	}
+	go s.ListenAndServeTLS("", "")
+	defer s.Close()
+
+	if _, err := p.client.Accept(ctx, chal); err != nil {
+		return fmt.Errorf("Accept(%q): %v", chal.URI, err)
+	}
+	_, zerr := p.client.WaitAuthorization(ctx, z.URI)
+	return zerr
+}
+
+func (p *prober) runHTTP01(ctx context.Context, z *acme.Authorization, chal *acme.Challenge) error {
+	body, err := p.client.HTTP01ChallengeResponse(chal.Token)
+	if err != nil {
+		return fmt.Errorf("HTTP01ChallengeResponse: %v", err)
+	}
+	s := &http.Server{
+		Addr: p.localAddr,
+		Handler: http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			log.Printf("%s %s", r.Method, r.URL)
+			if r.URL.Path != p.client.HTTP01ChallengePath(chal.Token) {
+				w.WriteHeader(http.StatusNotFound)
+				return
+			}
+			w.Write([]byte(body))
+		}),
+	}
+	go s.ListenAndServe()
+	defer s.Close()
+
+	if _, err := p.client.Accept(ctx, chal); err != nil {
+		return fmt.Errorf("Accept(%q): %v", chal.URI, err)
+	}
+	_, zerr := p.client.WaitAuthorization(ctx, z.URI)
+	return zerr
+}
+
+func (p *prober) runDNS01(ctx context.Context, z *acme.Authorization, chal *acme.Challenge) error {
+	token, err := p.client.DNS01ChallengeRecord(chal.Token)
+	if err != nil {
+		return fmt.Errorf("DNS01ChallengeRecord: %v", err)
+	}
+
+	name := fmt.Sprintf("_acme-challenge.%s", z.Identifier.Value)
+	cmd := exec.CommandContext(ctx, p.dnsScript, name, token)
+	cmd.Stdin = os.Stdin
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+	if err := cmd.Run(); err != nil {
+		return fmt.Errorf("%s: %v", p.dnsScript, err)
+	}
+
+	if _, err := p.client.Accept(ctx, chal); err != nil {
+		return fmt.Errorf("Accept(%q): %v", chal.URI, err)
+	}
+	_, zerr := p.client.WaitAuthorization(ctx, z.URI)
+	return zerr
+}
+
+func authorize(ctx context.Context, client *acme.Client, id acme.AuthzID) (*acme.Authorization, error) {
+	if id.Type == "ip" {
+		return client.AuthorizeIP(ctx, id.Value)
+	}
+	return client.Authorize(ctx, id.Value)
+}
+
+func checkCert(derChain [][]byte, id []acme.AuthzID) error {
+	if len(derChain) == 0 {
+		return errors.New("cert chain is zero bytes")
+	}
+	for i, b := range derChain {
+		crt, err := x509.ParseCertificate(b)
+		if err != nil {
+			return fmt.Errorf("%d: ParseCertificate: %v", i, err)
+		}
+		log.Printf("%d: serial: 0x%s", i, crt.SerialNumber)
+		log.Printf("%d: subject: %s", i, crt.Subject)
+		log.Printf("%d: issuer: %s", i, crt.Issuer)
+		log.Printf("%d: expires in %.1f day(s)", i, time.Until(crt.NotAfter).Hours()/24)
+		if i > 0 { // not a leaf cert
+			continue
+		}
+		p := &pem.Block{Type: "CERTIFICATE", Bytes: b}
+		log.Printf("%d: leaf:\n%s", i, pem.EncodeToMemory(p))
+		for _, v := range id {
+			if err := crt.VerifyHostname(v.Value); err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
+func newCSR(identifiers []acme.AuthzID) ([]byte, crypto.Signer) {
+	var csr x509.CertificateRequest
+	for _, id := range identifiers {
+		switch id.Type {
+		case "dns":
+			csr.DNSNames = append(csr.DNSNames, id.Value)
+		case "ip":
+			csr.IPAddresses = append(csr.IPAddresses, net.ParseIP(id.Value))
+		default:
+			panic(fmt.Sprintf("newCSR: unknown identifier type %q", id.Type))
+		}
+	}
+	k, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
+	if err != nil {
+		panic(fmt.Sprintf("newCSR: ecdsa.GenerateKey for a cert: %v", err))
+	}
+	b, err := x509.CreateCertificateRequest(rand.Reader, &csr, k)
+	if err != nil {
+		panic(fmt.Sprintf("newCSR: x509.CreateCertificateRequest: %v", err))
+	}
+	return b, k
+}