[ADD] Possibility to regenerate key

otp.go

@@ -46,6 +46,9 @@ var ErrGenerateMissingIssuer = errors.New("Issuer must be set")
 // When generating a Key, the Account Name must be set.
 var ErrGenerateMissingAccountName = errors.New("AccountName must be set")
 
+// When regenerating a Key, the Secret must be set.
+var ErrRegenerateMissingSecret = errors.New("Secret must be set")
+
 // Key represents an TOTP or HTOP key.
 type Key struct {
 	orig string
@@ -55,8 +58,8 @@ type Key struct {
 // NewKeyFromURL creates a new Key from an TOTP or HOTP url.
 //
 // The URL format is documented here:
-//   https://github.com/google/google-authenticator/wiki/Key-Uri-Format
 //
+//	https://github.com/google/google-authenticator/wiki/Key-Uri-Format
 func NewKeyFromURL(orig string) (*Key, error) {
 	s := strings.TrimSpace(orig)
 

totp/totp.go

@@ -18,10 +18,11 @@
 package totp
 
 import (
+	"io"
+
 	"github.com/pquerna/otp"
 	"github.com/pquerna/otp/hotp"
 	"github.com/pquerna/otp/internal"
-	"io"
 
 	"crypto/rand"
 	"encoding/base32"
@@ -205,3 +206,17 @@ func Generate(opts GenerateOpts) (*otp.Key, error) {
 
 	return otp.NewKeyFromURL(u.String())
 }
+
+// Restores a key from a secret opts.Secret must be set
+func Regenerate(opts GenerateOpts) (*otp.Key, error) {
+	if opts.SecretSize == 0 {
+		return nil, otp.ErrRegenerateMissingSecret
+	}
+	var secret []byte
+	_, err := base32.StdEncoding.Decode(secret, opts.Secret)
+	if err != nil {
+		return nil, err
+	}
+	opts.Secret = secret
+	return Generate(opts)
+}