mfa: better OTP registration flow on CLI (#6567)

Several improvements:
- show a QR code in the system image viewer
- print an OTP URL in addition to individual fields (some apps accept
  that as input)
- use cluster name as `Issuer` instead of "Teleport"

api/types/authentication.go

@@ -202,7 +202,7 @@ func (c *AuthPreferenceV2) SetConnectorName(cn string) {
 // GetU2F gets the U2F configuration settings.
 func (c *AuthPreferenceV2) GetU2F() (*U2F, error) {
 	if c.Spec.U2F == nil {
-		return nil, trace.NotFound("U2F configuration not found")
+		return nil, trace.NotFound("U2F is not configured in this cluster, please contact your administrator and ask them to follow https://goteleport.com/docs/access-controls/guides/u2f/")
 	}
 	return c.Spec.U2F, nil
 }

lib/auth/resetpasswordtoken.go

@@ -253,11 +253,13 @@ func (s *Server) newTOTPKey(user string) (*otp.Key, *totp.GenerateOpts, error) {
 	if err != nil {
 		return nil, nil, trace.Wrap(err)
 	}
+	clusterName, err := s.GetClusterName()
+	if err != nil {
+		return nil, nil, trace.Wrap(err)
+	}
 
 	opts := totp.GenerateOpts{
-		// TODO(awly): use proxy public addr as "Issuer", to distinguish
-		// between TOTP keys for different clusters.
-		Issuer:      "Teleport",
+		Issuer:      clusterName.GetClusterName(),
 		AccountName: accountName,
 		Period:      30, // seconds
 		Digits:      otp.DigitsSix,

tool/tsh/mfa.go

@@ -18,13 +18,20 @@ package main
 
 import (
 	"context"
+	"encoding/base32"
 	"fmt"
+	"image/png"
+	"io/ioutil"
 	"os"
+	"os/exec"
+	"runtime"
 	"strings"
 	"time"
 
 	"github.com/gravitational/kingpin"
 	"github.com/gravitational/trace"
+	"github.com/pquerna/otp"
+	"github.com/pquerna/otp/totp"
 
 	"github.com/gravitational/teleport/api/client/proto"
 	"github.com/gravitational/teleport/api/types"
@@ -278,20 +285,74 @@ func promptRegisterChallenge(ctx context.Context, proxyAddr string, c *proto.MFA
 }
 
 func promptTOTPRegisterChallenge(c *proto.TOTPRegisterChallenge) (*proto.MFARegisterResponse, error) {
-	// TODO(awly): mfa: use OS-specific image viewer to show a QR code.
-	// TODO(awly): mfa: print OTP URL
-	fmt.Println("Open your TOTP app and create a new manual entry with these fields:")
-	fmt.Printf("Name: %s\n", c.Account)
-	fmt.Printf("Issuer: %s\n", c.Issuer)
-	fmt.Printf("Algorithm: %s\n", c.Algorithm)
-	fmt.Printf("Number of digits: %d\n", c.Digits)
-	fmt.Printf("Period: %ds\n", c.PeriodSeconds)
-	fmt.Printf("Secret: %s\n", c.Secret)
-	fmt.Println()
+	secretBin, err := base32.StdEncoding.WithPadding(base32.NoPadding).DecodeString(c.Secret)
+	if err != nil {
+		return nil, trace.BadParameter("server sent an invalid TOTP secret key %q: %v", c.Secret, err)
+	}
+	var algorithm otp.Algorithm
+	switch strings.ToUpper(c.Algorithm) {
+	case "SHA1":
+		algorithm = otp.AlgorithmSHA1
+	case "SHA256":
+		algorithm = otp.AlgorithmSHA256
+	case "SHA512":
+		algorithm = otp.AlgorithmSHA512
+	case "MD5":
+		algorithm = otp.AlgorithmMD5
+	default:
+		return nil, trace.BadParameter("server sent an unknown TOTP algorithm %q", c.Algorithm)
+	}
+	otpKey, err := totp.Generate(totp.GenerateOpts{
+		Issuer:      c.Issuer,
+		AccountName: c.Account,
+		Period:      uint(c.PeriodSeconds),
+		Secret:      secretBin,
+		Digits:      otp.Digits(c.Digits),
+		Algorithm:   algorithm,
+	})
+	if err != nil {
+		return nil, trace.BadParameter("server sent invalid TOTP parameters: %v", err)
+	}
 
-	totpCode, err := prompt.Input(os.Stdout, os.Stdin, "Once created, enter an OTP code generated by the app")
+	// Try to show a QR code in the system image viewer.
+	// This is not supported on all platforms.
+	var showingQRCode bool
+	closeQR, err := showOTPQRCode(otpKey)
 	if err != nil {
-		return nil, trace.Wrap(err)
+		log.WithError(err).Debug("Failed to show QR code")
+	} else {
+		showingQRCode = true
+		defer closeQR()
+	}
+
+	fmt.Println()
+	if showingQRCode {
+		fmt.Println("Open your TOTP app and scan the QR code. Alternatively, you can manually enter these fields:")
+	} else {
+		fmt.Println("Open your TOTP app and create a new manual entry with these fields:")
+	}
+	fmt.Printf(`  URL: %s
+  Account name: %s
+  Secret key: %s
+  Issuer: %s
+  Algorithm: %s
+  Number of digits: %d
+  Period: %ds
+`, otpKey.URL(), c.Account, c.Secret, c.Issuer, c.Algorithm, c.Digits, c.PeriodSeconds)
+	fmt.Println()
+
+	var totpCode string
+	// Help the user with typos, don't submit the code until it has the right
+	// length.
+	for {
+		totpCode, err = prompt.Input(os.Stdout, os.Stdin, "Once created, enter an OTP code generated by the app")
+		if err != nil {
+			return nil, trace.Wrap(err)
+		}
+		if len(totpCode) == int(c.Digits) {
+			break
+		}
+		fmt.Printf("TOTP code must be exactly %d digits long, try again\n", c.Digits)
 	}
 	return &proto.MFARegisterResponse{Response: &proto.MFARegisterResponse_TOTP{
 		TOTP: &proto.TOTPRegisterResponse{Code: totpCode},
@@ -398,3 +459,52 @@ func (c *mfaRemoveCommand) run(cf *CLIConf) error {
 	fmt.Printf("MFA device %q removed.\n", c.name)
 	return nil
 }
+
+func showOTPQRCode(k *otp.Key) (cleanup func(), retErr error) {
+	var imageViewer string
+	switch runtime.GOOS {
+	case "linux":
+		imageViewer = "xdg-open"
+	case "darwin":
+		imageViewer = "open"
+	default:
+		return func() {}, trace.NotImplemented("showing QR codes is not implemented on %s", runtime.GOOS)
+	}
+
+	otpImage, err := k.Image(456, 456)
+	if err != nil {
+		return nil, trace.Wrap(err)
+	}
+	imageFile, err := ioutil.TempFile("", "teleport-otp-qr-code-*.png")
+	if err != nil {
+		return nil, trace.ConvertSystemError(err)
+	}
+	defer func() {
+		if retErr != nil {
+			imageFile.Close()
+			os.Remove(imageFile.Name())
+		}
+	}()
+
+	if err := png.Encode(imageFile, otpImage); err != nil {
+		return nil, trace.ConvertSystemError(err)
+	}
+	if err := imageFile.Close(); err != nil {
+		return nil, trace.ConvertSystemError(err)
+	}
+	log.Debugf("Wrote OTP QR code to %s", imageFile.Name())
+
+	cmd := exec.Command(imageViewer, imageFile.Name())
+	if err := cmd.Start(); err != nil {
+		return nil, trace.ConvertSystemError(err)
+	}
+	log.Debugf("Opened QR code via %q", imageViewer)
+	return func() {
+		if err := os.Remove(imageFile.Name()); err != nil {
+			log.WithError(err).Debugf("Failed to clean up temporary QR code file %q", imageFile.Name())
+		}
+		if err := cmd.Process.Kill(); err != nil {
+			log.WithError(err).Debug("Failed to stop the QR code image viewer")
+		}
+	}, nil
+}