feat(totp): secret customization (#2681)

Allow customizing the shared secrets size specifically for apps which don't support 256bit shared secrets.

config.template.yml

@@ -127,6 +127,9 @@ totp:
   skew: 1
   ## See: https://www.authelia.com/docs/configuration/one-time-password.html#input-validation to read the documentation.
 
+  ## The size of the generated shared secrets. Default is 32 and is sufficient in most use cases, minimum is 20.
+  secret_size: 32
+
 ##
 ## WebAuthn Configuration
 ##

docs/configuration/one-time-password.md

@@ -7,9 +7,9 @@ nav_order: 16
 
 # Time-based One-Time Password
 
-Authelia uses time-based one-time passwords as the OTP method. You have
+The OTP method _Authelia_ uses is the Time-Based One-Time Password Algorithm (TOTP) [RFC6238] which is an extension of
-the option to tune the settings of the TOTP generation, and you can see a
+HMAC-Based One-Time Password Algorithm (HOTP) [RFC4226]. You have the option to tune the settings of theTOTP generation, 
-full example of TOTP configuration below, as well as sections describing them.
+and you can see a full example of TOTP configuration below, as well as sections describing them.
 
 ## Configuration
 ```yaml
@@ -20,6 +20,7 @@ totp:
   digits: 6
   period: 30
   skew: 1
+  secret_size: 32
 ```
 
 ## Options
@@ -139,6 +140,21 @@ other.
 
 Changing this value affects all TOTP validations, not just newly registered ones.
 
+### secret_size
+<div markdown="1">
+type: integer
+{: .label .label-config .label-purple } 
+default: 32
+{: .label .label-config .label-blue }
+required: no
+{: .label .label-config .label-green }
+</div>
+
+The length in bytes of generated shared secrets. The minimum is 20 (or 160 bits), and the default is 32 (or 256 bits). 
+In most use cases 32 is sufficient. Though some authenticators may have issues with more than the minimum. Our minimum
+is the recommended value in [RFC4226], though technically according to the specification 16 bytes (or 128 bits) is the
+minimum.
+
 ## Registration
 When users register their TOTP device for the first time, the current [issuer](#issuer), [algorithm](#algorithm), and 
 [period](#period) are used to generate the TOTP link and QR code. These values are saved to the database for future
@@ -153,9 +169,8 @@ users to register a new device, you can delete the old device for a particular u
 The period and skew configuration parameters affect each other. The default values are a period of 30 and a skew of 1. 
 It is highly recommended you do not change these unless you wish to set skew to 0.
 
-The way you configure these affects security by changing the length of time a one-time
+These options affect security by changing the length of time a one-time password is valid for. The formula to calculate
-password is valid for. The formula to calculate the effective validity period is
+the effective validity period is `period + (period * skew * 2)`. For example period 30 and skew 1 would result in 90
-`period + (period * skew * 2)`. For example period 30 and skew 1 would result in 90
 seconds of validity, and period 30 and skew 2 would result in 150 seconds of validity.
 
 ## System time accuracy
@@ -192,3 +207,6 @@ Help:
 ```shell
 $ authelia storage totp export --help
 ```
+
+[RFC4226]: https://datatracker.ietf.org/doc/html/rfc4226
+[RFC6238]: https://datatracker.ietf.org/doc/html/rfc6238

internal/commands/storage.go

@@ -2,6 +2,8 @@ package commands
 
 import (
 	"github.com/spf13/cobra"
+
+	"github.com/authelia/authelia/v4/internal/configuration/schema"
 )
 
 // NewStorageCmd returns a new storage *cobra.Command.
@@ -107,6 +109,8 @@ func newStorageTOTPGenerateCmd() (cmd *cobra.Command) {
 		Args:  cobra.ExactArgs(1),
 	}
 
+	cmd.Flags().String("secret", "", "Optionally set the TOTP shared secret as base32 encoded bytes (no padding), it's recommended to not set this option unless you're restoring an TOTP config")
+	cmd.Flags().Uint("secret-size", schema.TOTPSecretSizeDefault, "set the TOTP secret size")
 	cmd.Flags().Uint("period", 30, "set the TOTP period")
 	cmd.Flags().Uint("digits", 6, "set the TOTP digits")
 	cmd.Flags().String("algorithm", "SHA1", "set the TOTP algorithm")

internal/commands/storage_run.go

@@ -2,6 +2,7 @@ package commands
 
 import (
 	"context"
+	"encoding/base32"
 	"errors"
 	"fmt"
 	"image"
@@ -11,6 +12,7 @@ import (
 	"strings"
 
 	"github.com/spf13/cobra"
+	"github.com/spf13/pflag"
 
 	"github.com/authelia/authelia/v4/internal/configuration"
 	"github.com/authelia/authelia/v4/internal/configuration/schema"
@@ -67,6 +69,7 @@ func storagePersistentPreRunE(cmd *cobra.Command, _ []string) (err error) {
 		"digits":      "totp.digits",
 		"algorithm":   "totp.algorithm",
 		"issuer":      "totp.issuer",
+		"secret-size": "totp.secret_size",
 	}
 
 	sources = append(sources, configuration.NewEnvironmentSource(configuration.DefaultEnvPrefix, configuration.DefaultEnvDelimiter))
@@ -205,7 +208,7 @@ func storageTOTPGenerateRunE(cmd *cobra.Command, args []string) (err error) {
 		ctx              = context.Background()
 		c                *model.TOTPConfiguration
 		force            bool
-		filename string
+		filename, secret string
 		file             *os.File
 		img              image.Image
 	)
@@ -216,25 +219,19 @@ func storageTOTPGenerateRunE(cmd *cobra.Command, args []string) (err error) {
 		_ = provider.Close()
 	}()
 
-	if force, err = cmd.Flags().GetBool("force"); err != nil {
+	if force, filename, secret, err = storageTOTPGenerateRunEOptsFromFlags(cmd.Flags()); err != nil {
-		return err
-	}
-
-	if filename, err = cmd.Flags().GetString("path"); err != nil {
 		return err
 	}
 
 	if _, err = provider.LoadTOTPConfiguration(ctx, args[0]); err == nil && !force {
 		return fmt.Errorf("%s already has a TOTP configuration, use --force to overwrite", args[0])
-	}
+	} else if err != nil && !errors.Is(err, storage.ErrNoTOTPConfiguration) {
-
-	if err != nil && !errors.Is(err, storage.ErrNoTOTPConfiguration) {
 		return err
 	}
 
 	totpProvider := totp.NewTimeBasedProvider(config.TOTP)
 
-	if c, err = totpProvider.Generate(args[0]); err != nil {
+	if c, err = totpProvider.GenerateCustom(args[0], config.TOTP.Algorithm, secret, config.TOTP.Digits, config.TOTP.Period, config.TOTP.SecretSize); err != nil {
 		return err
 	}
 
@@ -271,6 +268,28 @@ func storageTOTPGenerateRunE(cmd *cobra.Command, args []string) (err error) {
 	return nil
 }
 
+func storageTOTPGenerateRunEOptsFromFlags(flags *pflag.FlagSet) (force bool, filename, secret string, err error) {
+	if force, err = flags.GetBool("force"); err != nil {
+		return force, filename, secret, err
+	}
+
+	if filename, err = flags.GetString("path"); err != nil {
+		return force, filename, secret, err
+	}
+
+	if secret, err = flags.GetString("secret"); err != nil {
+		return force, filename, secret, err
+	}
+
+	secretLength := base32.StdEncoding.WithPadding(base32.NoPadding).DecodedLen(len(secret))
+	if secret != "" && secretLength < schema.TOTPSecretSizeMinimum {
+		return force, filename, secret, fmt.Errorf("decoded length of the base32 secret must have "+
+			"a length of more than %d but '%s' has a decoded length of %d", schema.TOTPSecretSizeMinimum, secret, secretLength)
+	}
+
+	return force, filename, secret, nil
+}
+
 func storageTOTPDeleteRunE(cmd *cobra.Command, args []string) (err error) {
 	var (
 		provider storage.Provider

internal/configuration/config.template.yml

@@ -127,6 +127,9 @@ totp:
   skew: 1
   ## See: https://www.authelia.com/docs/configuration/one-time-password.html#input-validation to read the documentation.
 
+  ## The size of the generated shared secrets. Default is 32 and is sufficient in most use cases, minimum is 20.
+  secret_size: 32
+
 ##
 ## WebAuthn Configuration
 ##

internal/configuration/schema/const.go

@@ -44,3 +44,11 @@ var (
 	// TOTPPossibleAlgorithms is a list of valid TOTP Algorithms.
 	TOTPPossibleAlgorithms = []string{TOTPAlgorithmSHA1, TOTPAlgorithmSHA256, TOTPAlgorithmSHA512}
 )
+
+const (
+	// TOTPSecretSizeDefault is the default secret size.
+	TOTPSecretSizeDefault = 32
+
+	// TOTPSecretSizeMinimum is the minimum secret size.
+	TOTPSecretSizeMinimum = 20
+)

internal/configuration/schema/totp.go

@@ -8,6 +8,7 @@ type TOTPConfiguration struct {
 	Digits     uint   `koanf:"digits"`
 	Period     uint   `koanf:"period"`
 	Skew       *uint  `koanf:"skew"`
+	SecretSize uint   `koanf:"secret_size"`
 }
 
 var defaultOtpSkew = uint(1)
@@ -19,4 +20,5 @@ var DefaultTOTPConfiguration = TOTPConfiguration{
 	Digits:     6,
 	Period:     30,
 	Skew:       &defaultOtpSkew,
+	SecretSize: TOTPSecretSizeDefault,
 }

internal/configuration/validator/const.go

@@ -107,6 +107,7 @@ const (
 	errFmtTOTPInvalidAlgorithm  = "totp: option 'algorithm' must be one of '%s' but it is configured as '%s'"
 	errFmtTOTPInvalidPeriod     = "totp: option 'period' option must be 15 or more but it is configured as '%d'"
 	errFmtTOTPInvalidDigits     = "totp: option 'digits' must be 6 or 8 but it is configured as '%d'"
+	errFmtTOTPInvalidSecretSize = "totp: option 'secret_size' must be %d or higher but it is configured as '%d'" //nolint:gosec
 )
 
 // Storage Error constants.
@@ -325,6 +326,7 @@ var ValidKeys = []string{
 	"totp.digits",
 	"totp.period",
 	"totp.skew",
+	"totp.secret_size",
 
 	// Webauthn Keys.
 	"webauthn.disable",

internal/configuration/validator/totp.go

@@ -10,6 +10,10 @@ import (
 
 // ValidateTOTP validates and update TOTP configuration.
 func ValidateTOTP(config *schema.Configuration, validator *schema.StructValidator) {
+	if config.TOTP.Disable {
+		return
+	}
+
 	if config.TOTP.Issuer == "" {
 		config.TOTP.Issuer = schema.DefaultTOTPConfiguration.Issuer
 	}
@@ -39,4 +43,10 @@ func ValidateTOTP(config *schema.Configuration, validator *schema.StructValidato
 	if config.TOTP.Skew == nil {
 		config.TOTP.Skew = schema.DefaultTOTPConfiguration.Skew
 	}
+
+	if config.TOTP.SecretSize == 0 {
+		config.TOTP.SecretSize = schema.DefaultTOTPConfiguration.SecretSize
+	} else if config.TOTP.SecretSize < schema.TOTPSecretSizeMinimum {
+		validator.Push(fmt.Errorf(errFmtTOTPInvalidSecretSize, schema.TOTPSecretSizeMinimum, config.TOTP.SecretSize))
+	}
 }

internal/configuration/validator/totp_test.go

@@ -2,7 +2,6 @@ package validator
 
 import (
 	"fmt"
-	"strings"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -11,63 +10,112 @@ import (
 	"github.com/authelia/authelia/v4/internal/configuration/schema"
 )
 
-func TestShouldSetDefaultTOTPValues(t *testing.T) {
+func TestValidateTOTP(t *testing.T) {
-	validator := schema.NewStructValidator()
+	testCases := []struct {
-	config := &schema.Configuration{
+		desc     string
-		TOTP: schema.TOTPConfiguration{},
+		have     schema.TOTPConfiguration
-	}
+		expected schema.TOTPConfiguration
-
+		errs     []string
-	ValidateTOTP(config, validator)
+		warns    []string
-
+	}{
-	require.Len(t, validator.Errors(), 0)
+		{
-	assert.Equal(t, "Authelia", config.TOTP.Issuer)
+			desc:     "ShouldSetDefaultTOTPValues",
-	assert.Equal(t, schema.DefaultTOTPConfiguration.Algorithm, config.TOTP.Algorithm)
+			expected: schema.DefaultTOTPConfiguration,
-	assert.Equal(t, schema.DefaultTOTPConfiguration.Skew, config.TOTP.Skew)
+		},
-	assert.Equal(t, schema.DefaultTOTPConfiguration.Period, config.TOTP.Period)
+		{
-}
+			desc:     "ShouldNotSetDefaultTOTPValuesWhenDisabled",
-
+			have:     schema.TOTPConfiguration{Disable: true},
-func TestShouldNormalizeTOTPAlgorithm(t *testing.T) {
+			expected: schema.TOTPConfiguration{Disable: true},
-	validator := schema.NewStructValidator()
+		},
-
+		{
-	config := &schema.Configuration{
+			desc: "ShouldNormalizeTOTPAlgorithm",
-		TOTP: schema.TOTPConfiguration{
+			have: schema.TOTPConfiguration{
 				Algorithm:  "sha1",
+				Digits:     6,
+				Period:     30,
+				SecretSize: 32,
+				Skew:       schema.DefaultTOTPConfiguration.Skew,
+				Issuer:     "abc",
 			},
-	}
+			expected: schema.TOTPConfiguration{
-
+				Algorithm:  "SHA1",
-	ValidateTOTP(config, validator)
+				Digits:     6,
-
+				Period:     30,
-	assert.Len(t, validator.Errors(), 0)
+				SecretSize: 32,
-	assert.Equal(t, "SHA1", config.TOTP.Algorithm)
+				Skew:       schema.DefaultTOTPConfiguration.Skew,
-}
+				Issuer:     "abc",
-
+			},
-func TestShouldRaiseErrorWhenInvalidTOTPAlgorithm(t *testing.T) {
+		},
-	validator := schema.NewStructValidator()
+		{
-
+			desc: "ShouldRaiseErrorWhenInvalidTOTPAlgorithm",
-	config := &schema.Configuration{
+			have: schema.TOTPConfiguration{
-		TOTP: schema.TOTPConfiguration{
 				Algorithm:  "sha3",
+				Digits:     6,
+				Period:     30,
+				SecretSize: 32,
+				Skew:       schema.DefaultTOTPConfiguration.Skew,
+				Issuer:     "abc",
 			},
-	}
+			errs: []string{"totp: option 'algorithm' must be one of 'SHA1', 'SHA256', 'SHA512' but it is configured as 'SHA3'"},
-
+		},
-	ValidateTOTP(config, validator)
+		{
-
+			desc: "ShouldRaiseErrorWhenInvalidTOTPValue",
-	require.Len(t, validator.Errors(), 1)
+			have: schema.TOTPConfiguration{
-	assert.EqualError(t, validator.Errors()[0], fmt.Sprintf(errFmtTOTPInvalidAlgorithm, strings.Join(schema.TOTPPossibleAlgorithms, "', '"), "SHA3"))
+				Algorithm:  "sha3",
-}
-
-func TestShouldRaiseErrorWhenInvalidTOTPValues(t *testing.T) {
-	validator := schema.NewStructValidator()
-	config := &schema.Configuration{
-		TOTP: schema.TOTPConfiguration{
 				Period:     5,
 				Digits:     20,
+				SecretSize: 10,
+				Skew:       schema.DefaultTOTPConfiguration.Skew,
+				Issuer:     "abc",
+			},
+			errs: []string{
+				"totp: option 'algorithm' must be one of 'SHA1', 'SHA256', 'SHA512' but it is configured as 'SHA3'",
+				"totp: option 'period' option must be 15 or more but it is configured as '5'",
+				"totp: option 'digits' must be 6 or 8 but it is configured as '20'",
+				"totp: option 'secret_size' must be 20 or higher but it is configured as '10'",
+			},
 		},
 	}
 
+	for _, tc := range testCases {
+		t.Run(tc.desc, func(t *testing.T) {
+			validator := schema.NewStructValidator()
+			config := &schema.Configuration{TOTP: tc.have}
+
 			ValidateTOTP(config, validator)
 
-	require.Len(t, validator.Errors(), 2)
+			errs := validator.Errors()
-	assert.EqualError(t, validator.Errors()[0], fmt.Sprintf(errFmtTOTPInvalidPeriod, 5))
+			warns := validator.Warnings()
-	assert.EqualError(t, validator.Errors()[1], fmt.Sprintf(errFmtTOTPInvalidDigits, 20))
+
+			if len(tc.errs) == 0 {
+				assert.Len(t, errs, 0)
+				assert.Len(t, warns, 0)
+				assert.Equal(t, tc.expected.Disable, config.TOTP.Disable)
+				assert.Equal(t, tc.expected.Issuer, config.TOTP.Issuer)
+				assert.Equal(t, tc.expected.Algorithm, config.TOTP.Algorithm)
+				assert.Equal(t, tc.expected.Skew, config.TOTP.Skew)
+				assert.Equal(t, tc.expected.Period, config.TOTP.Period)
+				assert.Equal(t, tc.expected.SecretSize, config.TOTP.SecretSize)
+			} else {
+				expectedErrs := len(tc.errs)
+
+				require.Len(t, errs, expectedErrs)
+
+				for i := 0; i < expectedErrs; i++ {
+					t.Run(fmt.Sprintf("Err%d", i+1), func(t *testing.T) {
+						assert.EqualError(t, errs[i], tc.errs[i])
+					})
+				}
+			}
+
+			expectedWarns := len(tc.warns)
+			require.Len(t, warns, expectedWarns)
+
+			for i := 0; i < expectedWarns; i++ {
+				t.Run(fmt.Sprintf("Err%d", i+1), func(t *testing.T) {
+					assert.EqualError(t, warns[i], tc.warns[i])
+				})
+			}
+		})
+	}
 }

internal/mocks/totp.go

@@ -51,18 +51,18 @@ func (mr *MockTOTPMockRecorder) Generate(arg0 interface{}) *gomock.Call {
 }
 
 // GenerateCustom mocks base method.
-func (m *MockTOTP) GenerateCustom(arg0, arg1 string, arg2, arg3, arg4 uint) (*model.TOTPConfiguration, error) {
+func (m *MockTOTP) GenerateCustom(arg0, arg1, arg2 string, arg3, arg4, arg5 uint) (*model.TOTPConfiguration, error) {
 	m.ctrl.T.Helper()
-	ret := m.ctrl.Call(m, "GenerateCustom", arg0, arg1, arg2, arg3, arg4)
+	ret := m.ctrl.Call(m, "GenerateCustom", arg0, arg1, arg2, arg3, arg4, arg5)
 	ret0, _ := ret[0].(*model.TOTPConfiguration)
 	ret1, _ := ret[1].(error)
 	return ret0, ret1
 }
 
 // GenerateCustom indicates an expected call of GenerateCustom.
-func (mr *MockTOTPMockRecorder) GenerateCustom(arg0, arg1, arg2, arg3, arg4 interface{}) *gomock.Call {
+func (mr *MockTOTPMockRecorder) GenerateCustom(arg0, arg1, arg2, arg3, arg4, arg5 interface{}) *gomock.Call {
 	mr.mock.ctrl.T.Helper()
-	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "GenerateCustom", reflect.TypeOf((*MockTOTP)(nil).GenerateCustom), arg0, arg1, arg2, arg3, arg4)
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "GenerateCustom", reflect.TypeOf((*MockTOTP)(nil).GenerateCustom), arg0, arg1, arg2, arg3, arg4, arg5)
 }
 
 // Validate mocks base method.

internal/totp/provider.go

@@ -7,6 +7,6 @@ import (
 // Provider for TOTP functionality.
 type Provider interface {
 	Generate(username string) (config *model.TOTPConfiguration, err error)
-	GenerateCustom(username string, algorithm string, digits, period, secretSize uint) (config *model.TOTPConfiguration, err error)
+	GenerateCustom(username string, algorithm, secret string, digits, period, secretSize uint) (config *model.TOTPConfiguration, err error)
 	Validate(token string, config *model.TOTPConfiguration) (valid bool, err error)
 }

internal/totp/totp.go

@@ -1,6 +1,8 @@
 package totp
 
 import (
+	"encoding/base32"
+	"fmt"
 	"time"
 
 	"github.com/pquerna/otp"
@@ -32,13 +34,22 @@ type TimeBased struct {
 }
 
 // GenerateCustom generates a TOTP with custom options.
-func (p TimeBased) GenerateCustom(username, algorithm string, digits, period, secretSize uint) (config *model.TOTPConfiguration, err error) {
+func (p TimeBased) GenerateCustom(username, algorithm, secret string, digits, period, secretSize uint) (config *model.TOTPConfiguration, err error) {
 	var key *otp.Key
 
+	var secretData []byte
+
+	if secret != "" {
+		if secretData, err = base32.StdEncoding.WithPadding(base32.NoPadding).DecodeString(secret); err != nil {
+			return nil, fmt.Errorf("totp generate failed: error decoding base32 string: %w", err)
+		}
+	}
+
 	opts := totp.GenerateOpts{
 		Issuer:      p.config.Issuer,
 		AccountName: username,
 		Period:      period,
+		Secret:      secretData,
 		SecretSize:  secretSize,
 		Digits:      otp.Digits(digits),
 		Algorithm:   otpStringToAlgo(algorithm),
@@ -63,7 +74,7 @@ func (p TimeBased) GenerateCustom(username, algorithm string, digits, period, se
 
 // Generate generates a TOTP with default options.
 func (p TimeBased) Generate(username string) (config *model.TOTPConfiguration, err error) {
-	return p.GenerateCustom(username, p.config.Algorithm, p.config.Digits, p.config.Period, 32)
+	return p.GenerateCustom(username, p.config.Algorithm, "", p.config.Digits, p.config.Period, p.config.SecretSize)
 }
 
 // Validate the token against the given configuration.

internal/totp/totp_test.go

@@ -6,54 +6,115 @@ import (
 	"time"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 
 	"github.com/authelia/authelia/v4/internal/configuration/schema"
 )
 
 func TestTOTPGenerateCustom(t *testing.T) {
+	testCases := []struct {
+		desc                        string
+		username, algorithm, secret string
+		digits, period, secretSize  uint
+		err                         string
+	}{
+		{
+			desc:       "ShouldGenerateSHA1",
+			username:   "john",
+			algorithm:  "SHA1",
+			digits:     6,
+			period:     30,
+			secretSize: 32,
+		},
+		{
+			desc:       "ShouldGenerateLongSecret",
+			username:   "john",
+			algorithm:  "SHA1",
+			digits:     6,
+			period:     30,
+			secretSize: 42,
+		},
+		{
+			desc:       "ShouldGenerateSHA256",
+			username:   "john",
+			algorithm:  "SHA256",
+			digits:     6,
+			period:     30,
+			secretSize: 32,
+		},
+		{
+			desc:       "ShouldGenerateSHA512",
+			username:   "john",
+			algorithm:  "SHA512",
+			digits:     6,
+			period:     30,
+			secretSize: 32,
+		},
+		{
+			desc:       "ShouldGenerateWithSecret",
+			username:   "john",
+			algorithm:  "SHA512",
+			secret:     "ONTGOYLTMZQXGZDBONSGC43EMFZWMZ3BONTWMYLTMRQXGZBSGMYTEMZRMFYXGZDBONSA",
+			digits:     6,
+			period:     30,
+			secretSize: 32,
+		},
+		{
+			desc:       "ShouldGenerateWithBadSecretB32Data",
+			username:   "john",
+			algorithm:  "SHA512",
+			secret:     "@#UNH$IK!J@N#EIKJ@U!NIJKUN@#WIK",
+			digits:     6,
+			period:     30,
+			secretSize: 32,
+			err:        "totp generate failed: error decoding base32 string: illegal base32 data at input byte 0",
+		},
+		{
+			desc:       "ShouldGenerateWithBadSecretLength",
+			username:   "john",
+			algorithm:  "SHA512",
+			secret:     "ONTGOYLTMZQXGZD",
+			digits:     6,
+			period:     30,
+			secretSize: 0,
+		},
+	}
+
 	totp := NewTimeBasedProvider(schema.TOTPConfiguration{
 		Issuer:     "Authelia",
 		Algorithm:  "SHA1",
 		Digits:     6,
 		Period:     30,
+		SecretSize: 32,
 	})
 
-	assert.Equal(t, uint(1), totp.skew)
+	for _, tc := range testCases {
-
+		t.Run(tc.desc, func(t *testing.T) {
-	config, err := totp.GenerateCustom("john", "SHA1", 6, 30, 32)
+			c, err := totp.GenerateCustom(tc.username, tc.algorithm, tc.secret, tc.digits, tc.period, tc.secretSize)
+			if tc.err == "" {
 				assert.NoError(t, err)
+				require.NotNil(t, c)
+				assert.Equal(t, tc.period, c.Period)
+				assert.Equal(t, tc.digits, c.Digits)
+				assert.Equal(t, tc.algorithm, c.Algorithm)
 
-	assert.Equal(t, uint(6), config.Digits)
+				expectedSecretLen := int(tc.secretSize)
-	assert.Equal(t, uint(30), config.Period)
+				if tc.secret != "" {
-	assert.Equal(t, "SHA1", config.Algorithm)
+					expectedSecretLen = base32.StdEncoding.WithPadding(base32.NoPadding).DecodedLen(len(tc.secret))
+				}
 
-	assert.Less(t, time.Since(config.CreatedAt), time.Second)
+				secret := make([]byte, expectedSecretLen)
-	assert.Greater(t, time.Since(config.CreatedAt), time.Second*-1)
 
-	secret := make([]byte, base32.StdEncoding.WithPadding(base32.NoPadding).DecodedLen(len(config.Secret)))
+				n, err := base32.StdEncoding.WithPadding(base32.NoPadding).Decode(secret, c.Secret)
-
-	_, err = base32.StdEncoding.WithPadding(base32.NoPadding).Decode(secret, config.Secret)
 				assert.NoError(t, err)
-	assert.Len(t, secret, 32)
+				assert.Len(t, secret, expectedSecretLen)
-
+				assert.Equal(t, expectedSecretLen, n)
-	config, err = totp.GenerateCustom("john", "SHA1", 6, 30, 42)
+			} else {
-	assert.NoError(t, err)
+				assert.Nil(t, c)
-
+				assert.EqualError(t, err, tc.err)
-	assert.Equal(t, uint(6), config.Digits)
+			}
-	assert.Equal(t, uint(30), config.Period)
+		})
-	assert.Equal(t, "SHA1", config.Algorithm)
+	}
-
-	assert.Less(t, time.Since(config.CreatedAt), time.Second)
-	assert.Greater(t, time.Since(config.CreatedAt), time.Second*-1)
-
-	secret = make([]byte, base32.StdEncoding.WithPadding(base32.NoPadding).DecodedLen(len(config.Secret)))
-
-	_, err = base32.StdEncoding.WithPadding(base32.NoPadding).Decode(secret, config.Secret)
-	assert.NoError(t, err)
-	assert.Len(t, secret, 42)
-
-	_, err = totp.GenerateCustom("", "SHA1", 6, 30, 32)
-	assert.EqualError(t, err, "AccountName must be set")
 }
 
 func TestTOTPGenerate(t *testing.T) {
@@ -65,6 +126,7 @@ func TestTOTPGenerate(t *testing.T) {
 		Digits:     8,
 		Period:     60,
 		Skew:       &skew,
+		SecretSize: 32,
 	})
 
 	assert.Equal(t, uint(2), totp.skew)