New validation API (#236)

* New Validation API

Some guidelines in designing the new validation API

* Previously, the `Valid` method was placed on the claim, which was always not entirely semantically correct, since the validity is concerning the token, not the claims. Although the validity of the token is based on the processing of the claims (such as `exp`). Therefore, the function `Valid` was removed from the `Claims` interface and the single canonical way to retrieve the validity of the token is to retrieve the `Valid` property of the `Token` struct.
* The previous fact was enhanced by the fact that most claims implementations had additional exported `VerifyXXX` functions, which are now removed
* All validation errors should be comparable with `errors.Is` to determine, why a particular validation has failed
* Developers want to adjust validation options. Popular options include:
  * Leeway when processing exp, nbf, iat
  * Not verifying `iat`, since this is actually just an informational claim. When purely looking at the standard, this should probably the default
  * Verifying `aud` by default, which actually the standard sort of demands. We need to see how strong we want to enforce this
* Developers want to create their own claim types, mostly by embedding one of the existing types such as `RegisteredClaims`.
  * Sometimes there is the need to further tweak the validation of a token by checking the value of a custom claim. Previously, this was possibly by overriding `Valid`. However, this was error-prone, e.g., if the original `Valid` was not called. Therefore, we should provide an easy way for *additional* checks, without by-passing the necessary validations

This leads to the following two major changes:

* The `Claims` interface now represents a set of functions that return the mandatory claims represented in a token, rather than just a `Valid` function. This is also more semantically correct.
* All validation tasks are offloaded to a new (optional) `validator`, which can also be configured with appropriate options. If no custom validator was supplied, a default one is used.

Co-authored-by: Micah Parks <66095735+MicahParks@users.noreply.github.com>

claims.go

@@ -1,173 +1,16 @@
 package jwt
 
-import (
-	"crypto/subtle"
-	"fmt"
-	"time"
-)
-
-// Claims must just have a Valid method that determines
-// if the token is invalid for any supported reason
+// Claims represent any form of a JWT Claims Set according to
+// https://datatracker.ietf.org/doc/html/rfc7519#section-4. In order to have a
+// common basis for validation, it is required that an implementation is able to
+// supply at least the claim names provided in
+// https://datatracker.ietf.org/doc/html/rfc7519#section-4.1 namely `exp`,
+// `iat`, `nbf`, `iss` and `aud`.
 type Claims interface {
-	Valid() error
-}
-
-// RegisteredClaims are a structured version of the JWT Claims Set,
-// restricted to Registered Claim Names, as referenced at
-// https://datatracker.ietf.org/doc/html/rfc7519#section-4.1
-//
-// This type can be used on its own, but then additional private and
-// public claims embedded in the JWT will not be parsed. The typical usecase
-// therefore is to embedded this in a user-defined claim type.
-//
-// See examples for how to use this with your own claim types.
-type RegisteredClaims struct {
-	// the `iss` (Issuer) claim. See https://datatracker.ietf.org/doc/html/rfc7519#section-4.1.1
-	Issuer string `json:"iss,omitempty"`
-
-	// the `sub` (Subject) claim. See https://datatracker.ietf.org/doc/html/rfc7519#section-4.1.2
-	Subject string `json:"sub,omitempty"`
-
-	// the `aud` (Audience) claim. See https://datatracker.ietf.org/doc/html/rfc7519#section-4.1.3
-	Audience ClaimStrings `json:"aud,omitempty"`
-
-	// the `exp` (Expiration Time) claim. See https://datatracker.ietf.org/doc/html/rfc7519#section-4.1.4
-	ExpiresAt *NumericDate `json:"exp,omitempty"`
-
-	// the `nbf` (Not Before) claim. See https://datatracker.ietf.org/doc/html/rfc7519#section-4.1.5
-	NotBefore *NumericDate `json:"nbf,omitempty"`
-
-	// the `iat` (Issued At) claim. See https://datatracker.ietf.org/doc/html/rfc7519#section-4.1.6
-	IssuedAt *NumericDate `json:"iat,omitempty"`
-
-	// the `jti` (JWT ID) claim. See https://datatracker.ietf.org/doc/html/rfc7519#section-4.1.7
-	ID string `json:"jti,omitempty"`
-}
-
-// Valid validates time based claims "exp, iat, nbf".
-// There is no accounting for clock skew.
-// As well, if any of the above claims are not in the token, it will still
-// be considered a valid claim.
-func (c RegisteredClaims) Valid() error {
-	vErr := new(ValidationError)
-	now := TimeFunc()
-
-	// The claims below are optional, by default, so if they are set to the
-	// default value in Go, let's not fail the verification for them.
-	if !c.VerifyExpiresAt(now, false) {
-		delta := now.Sub(c.ExpiresAt.Time)
-		vErr.Inner = fmt.Errorf("%s by %s", ErrTokenExpired, delta)
-		vErr.Errors |= ValidationErrorExpired
-	}
-
-	if !c.VerifyIssuedAt(now, false) {
-		vErr.Inner = ErrTokenUsedBeforeIssued
-		vErr.Errors |= ValidationErrorIssuedAt
-	}
-
-	if !c.VerifyNotBefore(now, false) {
-		vErr.Inner = ErrTokenNotValidYet
-		vErr.Errors |= ValidationErrorNotValidYet
-	}
-
-	if vErr.valid() {
-		return nil
-	}
-
-	return vErr
-}
-
-// VerifyAudience compares the aud claim against cmp.
-// If required is false, this method will return true if the value matches or is unset
-func (c *RegisteredClaims) VerifyAudience(cmp string, req bool) bool {
-	return verifyAud(c.Audience, cmp, req)
-}
-
-// VerifyExpiresAt compares the exp claim against cmp (cmp < exp).
-// If req is false, it will return true, if exp is unset.
-func (c *RegisteredClaims) VerifyExpiresAt(cmp time.Time, req bool) bool {
-	if c.ExpiresAt == nil {
-		return verifyExp(nil, cmp, req)
-	}
-
-	return verifyExp(&c.ExpiresAt.Time, cmp, req)
-}
-
-// VerifyIssuedAt compares the iat claim against cmp (cmp >= iat).
-// If req is false, it will return true, if iat is unset.
-func (c *RegisteredClaims) VerifyIssuedAt(cmp time.Time, req bool) bool {
-	if c.IssuedAt == nil {
-		return verifyIat(nil, cmp, req)
-	}
-
-	return verifyIat(&c.IssuedAt.Time, cmp, req)
-}
-
-// VerifyNotBefore compares the nbf claim against cmp (cmp >= nbf).
-// If req is false, it will return true, if nbf is unset.
-func (c *RegisteredClaims) VerifyNotBefore(cmp time.Time, req bool) bool {
-	if c.NotBefore == nil {
-		return verifyNbf(nil, cmp, req)
-	}
-
-	return verifyNbf(&c.NotBefore.Time, cmp, req)
-}
-
-// VerifyIssuer compares the iss claim against cmp.
-// If required is false, this method will return true if the value matches or is unset
-func (c *RegisteredClaims) VerifyIssuer(cmp string, req bool) bool {
-	return verifyIss(c.Issuer, cmp, req)
-}
-
-// ----- helpers
-
-func verifyAud(aud []string, cmp string, required bool) bool {
-	if len(aud) == 0 {
-		return !required
-	}
-	// use a var here to keep constant time compare when looping over a number of claims
-	result := false
-
-	var stringClaims string
-	for _, a := range aud {
-		if subtle.ConstantTimeCompare([]byte(a), []byte(cmp)) != 0 {
-			result = true
-		}
-		stringClaims = stringClaims + a
-	}
-
-	// case where "" is sent in one or many aud claims
-	if len(stringClaims) == 0 {
-		return !required
-	}
-
-	return result
-}
-
-func verifyExp(exp *time.Time, now time.Time, required bool) bool {
-	if exp == nil {
-		return !required
-	}
-	return now.Before(*exp)
-}
-
-func verifyIat(iat *time.Time, now time.Time, required bool) bool {
-	if iat == nil {
-		return !required
-	}
-	return now.After(*iat) || now.Equal(*iat)
-}
-
-func verifyNbf(nbf *time.Time, now time.Time, required bool) bool {
-	if nbf == nil {
-		return !required
-	}
-	return now.After(*nbf) || now.Equal(*nbf)
-}
-
-func verifyIss(iss string, cmp string, required bool) bool {
-	if iss == "" {
-		return !required
-	}
-	return subtle.ConstantTimeCompare([]byte(iss), []byte(cmp)) != 0
+	GetExpirationTime() (*NumericDate, error)
+	GetIssuedAt() (*NumericDate, error)
+	GetNotBefore() (*NumericDate, error)
+	GetIssuer() (string, error)
+	GetSubject() (string, error)
+	GetAudience() (ClaimStrings, error)
 }

errors.go

@@ -18,6 +18,7 @@ var (
 	ErrTokenExpired          = errors.New("token is expired")
 	ErrTokenUsedBeforeIssued = errors.New("token used before issued")
 	ErrTokenInvalidIssuer    = errors.New("token has invalid issuer")
+	ErrTokenInvalidSubject   = errors.New("token has invalid subject")
 	ErrTokenNotValidYet      = errors.New("token is not valid yet")
 	ErrTokenInvalidId        = errors.New("token has invalid id")
 	ErrTokenInvalidClaims    = errors.New("token has invalid claims")
@@ -29,11 +30,12 @@ const (
 	ValidationErrorUnverifiable                        // Token could not be verified because of signing problems
 	ValidationErrorSignatureInvalid                    // Signature validation failed
 
-	// Standard Claim validation errors
+	// Registered Claim validation errors
 	ValidationErrorAudience      // AUD validation failed
 	ValidationErrorExpired       // EXP validation failed
 	ValidationErrorIssuedAt      // IAT validation failed
 	ValidationErrorIssuer        // ISS validation failed
+	ValidationErrorSubject       // SUB validation failed
 	ValidationErrorNotValidYet   // NBF validation failed
 	ValidationErrorId            // JTI validation failed
 	ValidationErrorClaimsInvalid // Generic claims validation error

example_test.go

@@ -70,7 +70,7 @@ func ExampleNewWithClaims_customClaimsType() {
 	//Output: eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJmb28iOiJiYXIiLCJpc3MiOiJ0ZXN0IiwiZXhwIjoxNTE2MjM5MDIyfQ.xVuY2FZ_MRXMIEgVQ7J-TFtaucVFRXUzHm9LmV41goM <nil>
 }
 
-// Example creating a token using a custom claims type.  The StandardClaim is embedded
+// Example creating a token using a custom claims type.  The RegisteredClaims is embedded
 // in the custom type to allow for easy encoding, parsing and validation of standard claims.
 func ExampleParseWithClaims_customClaimsType() {
 	tokenString := "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJmb28iOiJiYXIiLCJpc3MiOiJ0ZXN0IiwiYXVkIjoic2luZ2xlIn0.QAWg1vGvnqRuCFTMcPkjZljXHh8U3L_qUjszOtQbeaA"
@@ -93,7 +93,63 @@ func ExampleParseWithClaims_customClaimsType() {
 	// Output: bar test
 }
 
-// An example of parsing the error types using bitfield checks
+// Example creating a token using a custom claims type and validation options.  The RegisteredClaims is embedded
+// in the custom type to allow for easy encoding, parsing and validation of standard claims.
+func ExampleParseWithClaims_validationOptions() {
+	tokenString := "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJmb28iOiJiYXIiLCJpc3MiOiJ0ZXN0IiwiYXVkIjoic2luZ2xlIn0.QAWg1vGvnqRuCFTMcPkjZljXHh8U3L_qUjszOtQbeaA"
+
+	type MyCustomClaims struct {
+		Foo string `json:"foo"`
+		jwt.RegisteredClaims
+	}
+
+	token, err := jwt.ParseWithClaims(tokenString, &MyCustomClaims{}, func(token *jwt.Token) (interface{}, error) {
+		return []byte("AllYourBase"), nil
+	}, jwt.WithLeeway(5*time.Second))
+
+	if claims, ok := token.Claims.(*MyCustomClaims); ok && token.Valid {
+		fmt.Printf("%v %v", claims.Foo, claims.RegisteredClaims.Issuer)
+	} else {
+		fmt.Println(err)
+	}
+
+	// Output: bar test
+}
+
+type MyCustomClaims struct {
+	Foo string `json:"foo"`
+	jwt.RegisteredClaims
+}
+
+func (m MyCustomClaims) CustomValidation() error {
+	if m.Foo != "bar" {
+		return errors.New("must be foobar")
+	}
+
+	return nil
+}
+
+// Example creating a token using a custom claims type and validation options.
+// The RegisteredClaims is embedded in the custom type to allow for easy
+// encoding, parsing and validation of standard claims and the function
+// CustomValidation is implemented.
+func ExampleParseWithClaims_customValidation() {
+	tokenString := "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJmb28iOiJiYXIiLCJpc3MiOiJ0ZXN0IiwiYXVkIjoic2luZ2xlIn0.QAWg1vGvnqRuCFTMcPkjZljXHh8U3L_qUjszOtQbeaA"
+
+	token, err := jwt.ParseWithClaims(tokenString, &MyCustomClaims{}, func(token *jwt.Token) (interface{}, error) {
+		return []byte("AllYourBase"), nil
+	}, jwt.WithLeeway(5*time.Second))
+
+	if claims, ok := token.Claims.(*MyCustomClaims); ok && token.Valid {
+		fmt.Printf("%v %v", claims.Foo, claims.RegisteredClaims.Issuer)
+	} else {
+		fmt.Println(err)
+	}
+
+	// Output: bar test
+}
+
+// An example of parsing the error types using errors.Is.
 func ExampleParse_errorChecking() {
 	// Token from another example.  This token is expired
 	var tokenString = "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJmb28iOiJiYXIiLCJleHAiOjE1MDAwLCJpc3MiOiJ0ZXN0In0.HE7fK0xOQwFEr4WDgRWj4teRPZ6i3GLwD5YCm6Pwu_c"

map_claims.go

@@ -3,149 +3,109 @@ package jwt
 import (
 	"encoding/json"
 	"errors"
-	"time"
-	// "fmt"
 )
 
 // MapClaims is a claims type that uses the map[string]interface{} for JSON decoding.
 // This is the default claims type if you don't supply one
 type MapClaims map[string]interface{}
 
-// VerifyAudience Compares the aud claim against cmp.
-// If required is false, this method will return true if the value matches or is unset
-func (m MapClaims) VerifyAudience(cmp string, req bool) bool {
-	var aud []string
-	switch v := m["aud"].(type) {
-	case string:
-		aud = append(aud, v)
-	case []string:
-		aud = v
-	case []interface{}:
-		for _, a := range v {
-			vs, ok := a.(string)
-			if !ok {
-				return false
-			}
-			aud = append(aud, vs)
-		}
-	}
-	return verifyAud(aud, cmp, req)
+var ErrInvalidType = errors.New("invalid type for claim")
+
+// GetExpirationTime implements the Claims interface.
+func (m MapClaims) GetExpirationTime() (*NumericDate, error) {
+	return m.ParseNumericDate("exp")
 }
 
-// VerifyExpiresAt compares the exp claim against cmp (cmp <= exp).
-// If req is false, it will return true, if exp is unset.
-func (m MapClaims) VerifyExpiresAt(cmp int64, req bool) bool {
-	cmpTime := time.Unix(cmp, 0)
+// GetNotBefore implements the Claims interface.
+func (m MapClaims) GetNotBefore() (*NumericDate, error) {
+	return m.ParseNumericDate("nbf")
+}
 
-	v, ok := m["exp"]
+// GetIssuedAt implements the Claims interface.
+func (m MapClaims) GetIssuedAt() (*NumericDate, error) {
+	return m.ParseNumericDate("iat")
+}
+
+// GetAudience implements the Claims interface.
+func (m MapClaims) GetAudience() (ClaimStrings, error) {
+	return m.ParseClaimsString("aud")
+}
+
+// GetIssuer implements the Claims interface.
+func (m MapClaims) GetIssuer() (string, error) {
+	return m.ParseString("iss")
+}
+
+// GetSubject implements the Claims interface.
+func (m MapClaims) GetSubject() (string, error) {
+	return m.ParseString("sub")
+}
+
+// ParseNumericDate tries to parse a key in the map claims type as a number
+// date. This will succeed, if the underlying type is either a [float64] or a
+// [json.Number]. Otherwise, nil will be returned.
+func (m MapClaims) ParseNumericDate(key string) (*NumericDate, error) {
+	v, ok := m[key]
 	if !ok {
-		return !req
+		return nil, nil
 	}
 
 	switch exp := v.(type) {
 	case float64:
 		if exp == 0 {
-			return verifyExp(nil, cmpTime, req)
+			return nil, nil
 		}
 
-		return verifyExp(&newNumericDateFromSeconds(exp).Time, cmpTime, req)
+		return newNumericDateFromSeconds(exp), nil
 	case json.Number:
 		v, _ := exp.Float64()
 
-		return verifyExp(&newNumericDateFromSeconds(v).Time, cmpTime, req)
+		return newNumericDateFromSeconds(v), nil
 	}
 
-	return false
+	return nil, ErrInvalidType
 }
 
-// VerifyIssuedAt compares the exp claim against cmp (cmp >= iat).
-// If req is false, it will return true, if iat is unset.
-func (m MapClaims) VerifyIssuedAt(cmp int64, req bool) bool {
-	cmpTime := time.Unix(cmp, 0)
-
-	v, ok := m["iat"]
-	if !ok {
-		return !req
-	}
-
-	switch iat := v.(type) {
-	case float64:
-		if iat == 0 {
-			return verifyIat(nil, cmpTime, req)
+// ParseClaimsString tries to parse a key in the map claims type as a
+// [ClaimsStrings] type, which can either be a string or an array of string.
+func (m MapClaims) ParseClaimsString(key string) (ClaimStrings, error) {
+	var cs []string
+	switch v := m[key].(type) {
+	case string:
+		cs = append(cs, v)
+	case []string:
+		cs = v
+	case []interface{}:
+		for _, a := range v {
+			vs, ok := a.(string)
+			if !ok {
+				return nil, ErrInvalidType
+			}
+			cs = append(cs, vs)
 		}
-
-		return verifyIat(&newNumericDateFromSeconds(iat).Time, cmpTime, req)
-	case json.Number:
-		v, _ := iat.Float64()
-
-		return verifyIat(&newNumericDateFromSeconds(v).Time, cmpTime, req)
 	}
 
-	return false
+	return cs, nil
 }
 
-// VerifyNotBefore compares the nbf claim against cmp (cmp >= nbf).
-// If req is false, it will return true, if nbf is unset.
-func (m MapClaims) VerifyNotBefore(cmp int64, req bool) bool {
-	cmpTime := time.Unix(cmp, 0)
-
-	v, ok := m["nbf"]
+// ParseString tries to parse a key in the map claims type as a [string] type.
+// If the key does not exist, an empty string is returned. If the key has the
+// wrong type, an error is returned.
+func (m MapClaims) ParseString(key string) (string, error) {
+	var (
+		ok  bool
+		raw interface{}
+		iss string
+	)
+	raw, ok = m[key]
 	if !ok {
-		return !req
+		return "", nil
 	}
 
-	switch nbf := v.(type) {
-	case float64:
-		if nbf == 0 {
-			return verifyNbf(nil, cmpTime, req)
-		}
-
-		return verifyNbf(&newNumericDateFromSeconds(nbf).Time, cmpTime, req)
-	case json.Number:
-		v, _ := nbf.Float64()
-
-		return verifyNbf(&newNumericDateFromSeconds(v).Time, cmpTime, req)
+	iss, ok = raw.(string)
+	if !ok {
+		return "", ErrInvalidType
 	}
 
-	return false
-}
-
-// VerifyIssuer compares the iss claim against cmp.
-// If required is false, this method will return true if the value matches or is unset
-func (m MapClaims) VerifyIssuer(cmp string, req bool) bool {
-	iss, _ := m["iss"].(string)
-	return verifyIss(iss, cmp, req)
-}
-
-// Valid validates time based claims "exp, iat, nbf".
-// There is no accounting for clock skew.
-// As well, if any of the above claims are not in the token, it will still
-// be considered a valid claim.
-func (m MapClaims) Valid() error {
-	vErr := new(ValidationError)
-	now := TimeFunc().Unix()
-
-	if !m.VerifyExpiresAt(now, false) {
-		// TODO(oxisto): this should be replaced with ErrTokenExpired
-		vErr.Inner = errors.New("Token is expired")
-		vErr.Errors |= ValidationErrorExpired
-	}
-
-	if !m.VerifyIssuedAt(now, false) {
-		// TODO(oxisto): this should be replaced with ErrTokenUsedBeforeIssued
-		vErr.Inner = errors.New("Token used before issued")
-		vErr.Errors |= ValidationErrorIssuedAt
-	}
-
-	if !m.VerifyNotBefore(now, false) {
-		// TODO(oxisto): this should be replaced with ErrTokenNotValidYet
-		vErr.Inner = errors.New("Token is not valid yet")
-		vErr.Errors |= ValidationErrorNotValidYet
-	}
-
-	if vErr.valid() {
-		return nil
-	}
-
-	return vErr
+	return iss, nil
 }

map_claims_test.go

@@ -42,7 +42,7 @@ func TestVerifyAud(t *testing.T) {
 		{Name: "[]String Aud without match not required", MapClaims: MapClaims{"aud": []string{"not.example.com", "example.example.com"}}, Expected: false, Required: true, Comparison: "example.com"},
 
 		// Required = false
-		{Name: "Empty []String Aud without match required", MapClaims: MapClaims{"aud": []string{""}}, Expected: false, Required: true, Comparison: "example.com"},
+		{Name: "Empty []String Aud without match required", MapClaims: MapClaims{"aud": []string{""}}, Expected: true, Required: false, Comparison: "example.com"},
 
 		// []interface{}
 		{Name: "Empty []interface{} Aud without match required", MapClaims: MapClaims{"aud": nilListInterface}, Expected: true, Required: false, Comparison: "example.com"},
@@ -56,10 +56,17 @@ func TestVerifyAud(t *testing.T) {
 
 	for _, test := range tests {
 		t.Run(test.Name, func(t *testing.T) {
-			got := test.MapClaims.VerifyAudience(test.Comparison, test.Required)
+			var opts []ParserOption
 
-			if got != test.Expected {
-				t.Errorf("Expected %v, got %v", test.Expected, got)
+			if test.Required {
+				opts = append(opts, WithAudience(test.Comparison))
+			}
+
+			validator := newValidator(opts...)
+			got := validator.Validate(test.MapClaims)
+
+			if (got == nil) != test.Expected {
+				t.Errorf("Expected %v, got %v", test.Expected, (got == nil))
 			}
 		})
 	}
@@ -70,9 +77,9 @@ func TestMapclaimsVerifyIssuedAtInvalidTypeString(t *testing.T) {
 		"iat": "foo",
 	}
 	want := false
-	got := mapClaims.VerifyIssuedAt(0, false)
-	if want != got {
-		t.Fatalf("Failed to verify claims, wanted: %v got %v", want, got)
+	got := newValidator(WithIssuedAt()).Validate(mapClaims)
+	if want != (got == nil) {
+		t.Fatalf("Failed to verify claims, wanted: %v got %v", want, (got == nil))
 	}
 }
 
@@ -81,9 +88,9 @@ func TestMapclaimsVerifyNotBeforeInvalidTypeString(t *testing.T) {
 		"nbf": "foo",
 	}
 	want := false
-	got := mapClaims.VerifyNotBefore(0, false)
-	if want != got {
-		t.Fatalf("Failed to verify claims, wanted: %v got %v", want, got)
+	got := newValidator().Validate(mapClaims)
+	if want != (got == nil) {
+		t.Fatalf("Failed to verify claims, wanted: %v got %v", want, (got == nil))
 	}
 }
 
@@ -92,32 +99,38 @@ func TestMapclaimsVerifyExpiresAtInvalidTypeString(t *testing.T) {
 		"exp": "foo",
 	}
 	want := false
-	got := mapClaims.VerifyExpiresAt(0, false)
+	got := newValidator().Validate(mapClaims)
 
-	if want != got {
-		t.Fatalf("Failed to verify claims, wanted: %v got %v", want, got)
+	if want != (got == nil) {
+		t.Fatalf("Failed to verify claims, wanted: %v got %v", want, (got == nil))
 	}
 }
 
 func TestMapClaimsVerifyExpiresAtExpire(t *testing.T) {
-	exp := time.Now().Unix()
+	exp := time.Now()
 	mapClaims := MapClaims{
-		"exp": float64(exp),
+		"exp": float64(exp.Unix()),
 	}
 	want := false
-	got := mapClaims.VerifyExpiresAt(exp, true)
-	if want != got {
-		t.Fatalf("Failed to verify claims, wanted: %v got %v", want, got)
+	got := newValidator(WithTimeFunc(func() time.Time {
+		return exp
+	})).Validate(mapClaims)
+	if want != (got == nil) {
+		t.Fatalf("Failed to verify claims, wanted: %v got %v", want, (got == nil))
 	}
 
-	got = mapClaims.VerifyExpiresAt(exp+1, true)
-	if want != got {
-		t.Fatalf("Failed to verify claims, wanted: %v got %v", want, got)
+	got = newValidator(WithTimeFunc(func() time.Time {
+		return exp.Add(1 * time.Second)
+	})).Validate(mapClaims)
+	if want != (got == nil) {
+		t.Fatalf("Failed to verify claims, wanted: %v got %v", want, (got == nil))
 	}
 
 	want = true
-	got = mapClaims.VerifyExpiresAt(exp-1, true)
-	if want != got {
-		t.Fatalf("Failed to verify claims, wanted: %v got %v", want, got)
+	got = newValidator(WithTimeFunc(func() time.Time {
+		return exp.Add(-1 * time.Second)
+	})).Validate(mapClaims)
+	if want != (got == nil) {
+		t.Fatalf("Failed to verify claims, wanted: %v got %v", want, (got == nil))
 	}
 }

parser.go

@@ -9,26 +9,24 @@ import (
 
 type Parser struct {
 	// If populated, only these methods will be considered valid.
-	//
-	// Deprecated: In future releases, this field will not be exported anymore and should be set with an option to NewParser instead.
-	ValidMethods []string
+	validMethods []string
 
 	// Use JSON Number format in JSON decoder.
-	//
-	// Deprecated: In future releases, this field will not be exported anymore and should be set with an option to NewParser instead.
-	UseJSONNumber bool
+	useJSONNumber bool
 
 	// Skip claims validation during token parsing.
-	//
-	// Deprecated: In future releases, this field will not be exported anymore and should be set with an option to NewParser instead.
-	SkipClaimsValidation bool
+	skipClaimsValidation bool
+
+	validator *validator
 }
 
 // NewParser creates a new Parser with the specified options
 func NewParser(options ...ParserOption) *Parser {
-	p := &Parser{}
+	p := &Parser{
+		validator: &validator{},
+	}
 
-	// loop through our parsing options and apply them
+	// Loop through our parsing options and apply them
 	for _, option := range options {
 		option(p)
 	}
@@ -56,10 +54,10 @@ func (p *Parser) ParseWithClaims(tokenString string, claims Claims, keyFunc Keyf
 	}
 
 	// Verify signing method is in the required set
-	if p.ValidMethods != nil {
+	if p.validMethods != nil {
 		var signingMethodValid = false
 		var alg = token.Method.Alg()
-		for _, m := range p.ValidMethods {
+		for _, m := range p.validMethods {
 			if m == alg {
 				signingMethodValid = true
 				break
@@ -88,9 +86,13 @@ func (p *Parser) ParseWithClaims(tokenString string, claims Claims, keyFunc Keyf
 	vErr := &ValidationError{}
 
 	// Validate Claims
-	if !p.SkipClaimsValidation {
-		if err := token.Claims.Valid(); err != nil {
+	if !p.skipClaimsValidation {
+		// Make sure we have at least a default validator
+		if p.validator == nil {
+			p.validator = newValidator()
+		}
 
+		if err := p.validator.Validate(claims); err != nil {
 			// If the Claims Valid returned an error, check if it is a validation error,
 			// If it was another error type, create a ValidationError with a generic ClaimsInvalid flag set
 			if e, ok := err.(*ValidationError); !ok {
@@ -150,7 +152,7 @@ func (p *Parser) ParseUnverified(tokenString string, claims Claims) (token *Toke
 		return token, parts, &ValidationError{Inner: err, Errors: ValidationErrorMalformed}
 	}
 	dec := json.NewDecoder(bytes.NewBuffer(claimBytes))
-	if p.UseJSONNumber {
+	if p.useJSONNumber {
 		dec.UseNumber()
 	}
 	// JSON Decode.  Special case for map type to avoid weird pointer behavior

parser_option.go

@@ -1,5 +1,7 @@
 package jwt
 
+import "time"
+
 // ParserOption is used to implement functional-style options that modify the behavior of the parser. To add
 // new options, just create a function (ideally beginning with With or Without) that returns an anonymous function that
 // takes a *Parser type as input and manipulates its configuration accordingly.
@@ -9,14 +11,14 @@ type ParserOption func(*Parser)
 // It is heavily encouraged to use this option in order to prevent attacks such as https://auth0.com/blog/critical-vulnerabilities-in-json-web-token-libraries/.
 func WithValidMethods(methods []string) ParserOption {
 	return func(p *Parser) {
-		p.ValidMethods = methods
+		p.validMethods = methods
 	}
 }
 
 // WithJSONNumber is an option to configure the underlying JSON parser with UseNumber
 func WithJSONNumber() ParserOption {
 	return func(p *Parser) {
-		p.UseJSONNumber = true
+		p.useJSONNumber = true
 	}
 }
 
@@ -24,6 +26,69 @@ func WithJSONNumber() ParserOption {
 // what you are doing.
 func WithoutClaimsValidation() ParserOption {
 	return func(p *Parser) {
-		p.SkipClaimsValidation = true
+		p.skipClaimsValidation = true
+	}
+}
+
+// WithLeeway returns the ParserOption for specifying the leeway window.
+func WithLeeway(leeway time.Duration) ParserOption {
+	return func(p *Parser) {
+		p.validator.leeway = leeway
+	}
+}
+
+// WithTimeFunc returns the ParserOption for specifying the time func. The
+// primary use-case for this is testing. If you are looking for a way to account
+// for clock-skew, WithLeeway should be used instead.
+func WithTimeFunc(f func() time.Time) ParserOption {
+	return func(p *Parser) {
+		p.validator.timeFunc = f
+	}
+}
+
+// WithIssuedAt returns the ParserOption to enable verification
+// of issued-at.
+func WithIssuedAt() ParserOption {
+	return func(p *Parser) {
+		p.validator.verifyIat = true
+	}
+}
+
+// WithAudience configures the validator to require the specified audience in
+// the `aud` claim. Validation will fail if the audience is not listed in the
+// token or the `aud` claim is missing.
+//
+// NOTE: While the `aud` claim is OPTIONAL is a JWT, the handling of it is
+// application-specific. Since this validation API is helping developers in
+// writing secure application, we decided to REQUIRE the existence of the claim.
+func WithAudience(aud string) ParserOption {
+	return func(p *Parser) {
+		p.validator.expectedAud = aud
+	}
+}
+
+// WithIssuer configures the validator to require the specified issuer in the
+// `iss` claim. Validation will fail if a different issuer is specified in the
+// token or the `iss` claim is missing.
+//
+// NOTE: While the `iss` claim is OPTIONAL is a JWT, the handling of it is
+// application-specific. Since this validation API is helping developers in
+// writing secure application, we decided to REQUIRE the existence of the claim.
+func WithIssuer(iss string) ParserOption {
+	return func(p *Parser) {
+		p.validator.expectedIss = iss
+	}
+}
+
+// WithSubject configures the validator to require the specified subject in the
+// `sub` claim. Validation will fail if a different subject is specified in the
+// token or the `sub` claim is missing.
+//
+// NOTE: While the `sub` claim is OPTIONAL is a JWT, the handling of it is
+// application-specific. Since this validation API is helping developers in
+// writing secure application, we decided to REQUIRE the existence of the claim.
+func WithSubject(sub string) ParserOption {
+	return func(p *Parser) {
+		p.validator.expectedSub = sub
 	}
 }

parser_test.go

@@ -152,7 +152,7 @@ var jwtTestData = []struct {
 		false,
 		jwt.ValidationErrorSignatureInvalid,
 		[]error{jwt.ErrTokenSignatureInvalid},
-		&jwt.Parser{ValidMethods: []string{"HS256"}},
+		jwt.NewParser(jwt.WithValidMethods([]string{"HS256"})),
 		jwt.SigningMethodRS256,
 	},
 	{
@@ -163,7 +163,7 @@ var jwtTestData = []struct {
 		true,
 		0,
 		nil,
-		&jwt.Parser{ValidMethods: []string{"RS256", "HS256"}},
+		jwt.NewParser(jwt.WithValidMethods([]string{"RS256", "HS256"})),
 		jwt.SigningMethodRS256,
 	},
 	{
@@ -174,7 +174,7 @@ var jwtTestData = []struct {
 		false,
 		jwt.ValidationErrorSignatureInvalid,
 		[]error{jwt.ErrTokenSignatureInvalid},
-		&jwt.Parser{ValidMethods: []string{"RS256", "HS256"}},
+		jwt.NewParser(jwt.WithValidMethods([]string{"RS256", "HS256"})),
 		jwt.SigningMethodES256,
 	},
 	{
@@ -185,7 +185,7 @@ var jwtTestData = []struct {
 		true,
 		0,
 		nil,
-		&jwt.Parser{ValidMethods: []string{"HS256", "ES256"}},
+		jwt.NewParser(jwt.WithValidMethods([]string{"HS256", "ES256"})),
 		jwt.SigningMethodES256,
 	},
 	{
@@ -196,7 +196,7 @@ var jwtTestData = []struct {
 		true,
 		0,
 		nil,
-		&jwt.Parser{UseJSONNumber: true},
+		jwt.NewParser(jwt.WithJSONNumber()),
 		jwt.SigningMethodRS256,
 	},
 	{
@@ -207,7 +207,7 @@ var jwtTestData = []struct {
 		false,
 		jwt.ValidationErrorExpired,
 		[]error{jwt.ErrTokenExpired},
-		&jwt.Parser{UseJSONNumber: true},
+		jwt.NewParser(jwt.WithJSONNumber()),
 		jwt.SigningMethodRS256,
 	},
 	{
@@ -218,7 +218,7 @@ var jwtTestData = []struct {
 		false,
 		jwt.ValidationErrorNotValidYet,
 		[]error{jwt.ErrTokenNotValidYet},
-		&jwt.Parser{UseJSONNumber: true},
+		jwt.NewParser(jwt.WithJSONNumber()),
 		jwt.SigningMethodRS256,
 	},
 	{
@@ -229,7 +229,7 @@ var jwtTestData = []struct {
 		false,
 		jwt.ValidationErrorNotValidYet | jwt.ValidationErrorExpired,
 		[]error{jwt.ErrTokenNotValidYet},
-		&jwt.Parser{UseJSONNumber: true},
+		jwt.NewParser(jwt.WithJSONNumber()),
 		jwt.SigningMethodRS256,
 	},
 	{
@@ -240,7 +240,7 @@ var jwtTestData = []struct {
 		true,
 		0,
 		nil,
-		&jwt.Parser{UseJSONNumber: true, SkipClaimsValidation: true},
+		jwt.NewParser(jwt.WithJSONNumber(), jwt.WithoutClaimsValidation()),
 		jwt.SigningMethodRS256,
 	},
 	{
@@ -253,7 +253,7 @@ var jwtTestData = []struct {
 		true,
 		0,
 		nil,
-		&jwt.Parser{UseJSONNumber: true},
+		jwt.NewParser(jwt.WithJSONNumber()),
 		jwt.SigningMethodRS256,
 	},
 	{
@@ -266,7 +266,7 @@ var jwtTestData = []struct {
 		true,
 		0,
 		nil,
-		&jwt.Parser{UseJSONNumber: true},
+		jwt.NewParser(jwt.WithJSONNumber()),
 		jwt.SigningMethodRS256,
 	},
 	{
@@ -279,7 +279,7 @@ var jwtTestData = []struct {
 		true,
 		0,
 		nil,
-		&jwt.Parser{UseJSONNumber: true},
+		jwt.NewParser(jwt.WithJSONNumber()),
 		jwt.SigningMethodRS256,
 	},
 	{
@@ -292,7 +292,7 @@ var jwtTestData = []struct {
 		false,
 		jwt.ValidationErrorMalformed,
 		[]error{jwt.ErrTokenMalformed},
-		&jwt.Parser{UseJSONNumber: true},
+		jwt.NewParser(jwt.WithJSONNumber()),
 		jwt.SigningMethodRS256,
 	},
 	{
@@ -305,7 +305,29 @@ var jwtTestData = []struct {
 		false,
 		jwt.ValidationErrorMalformed,
 		[]error{jwt.ErrTokenMalformed},
-		&jwt.Parser{UseJSONNumber: true},
+		jwt.NewParser(jwt.WithJSONNumber()),
+		jwt.SigningMethodRS256,
+	},
+	{
+		"RFC7519 Claims - nbf with 60s skew",
+		"", // autogen
+		defaultKeyFunc,
+		&jwt.RegisteredClaims{NotBefore: jwt.NewNumericDate(time.Now().Add(time.Second * 100))},
+		false,
+		jwt.ValidationErrorNotValidYet,
+		[]error{jwt.ErrTokenNotValidYet},
+		jwt.NewParser(jwt.WithLeeway(time.Minute)),
+		jwt.SigningMethodRS256,
+	},
+	{
+		"RFC7519 Claims - nbf with 120s skew",
+		"", // autogen
+		defaultKeyFunc,
+		&jwt.RegisteredClaims{NotBefore: jwt.NewNumericDate(time.Now().Add(time.Second * 100))},
+		true,
+		0,
+		nil,
+		jwt.NewParser(jwt.WithLeeway(2 * time.Minute)),
 		jwt.SigningMethodRS256,
 	},
 }
@@ -341,7 +363,7 @@ func TestParser_Parse(t *testing.T) {
 			var err error
 			var parser = data.parser
 			if parser == nil {
-				parser = new(jwt.Parser)
+				parser = jwt.NewParser()
 			}
 			// Figure out correct claims type
 			switch data.claims.(type) {
@@ -638,8 +660,7 @@ func TestSetPadding(t *testing.T) {
 			// Parse the token
 			var token *jwt.Token
 			var err error
-			parser := new(jwt.Parser)
-			parser.SkipClaimsValidation = true
+			parser := jwt.NewParser(jwt.WithoutClaimsValidation())
 
 			// Figure out correct claims type
 			token, err = parser.ParseWithClaims(data.tokenString, jwt.MapClaims{}, data.keyfunc)

registered_claims.go

@@ -0,0 +1,63 @@
+package jwt
+
+// RegisteredClaims are a structured version of the JWT Claims Set,
+// restricted to Registered Claim Names, as referenced at
+// https://datatracker.ietf.org/doc/html/rfc7519#section-4.1
+//
+// This type can be used on its own, but then additional private and
+// public claims embedded in the JWT will not be parsed. The typical use-case
+// therefore is to embedded this in a user-defined claim type.
+//
+// See examples for how to use this with your own claim types.
+type RegisteredClaims struct {
+	// the `iss` (Issuer) claim. See https://datatracker.ietf.org/doc/html/rfc7519#section-4.1.1
+	Issuer string `json:"iss,omitempty"`
+
+	// the `sub` (Subject) claim. See https://datatracker.ietf.org/doc/html/rfc7519#section-4.1.2
+	Subject string `json:"sub,omitempty"`
+
+	// the `aud` (Audience) claim. See https://datatracker.ietf.org/doc/html/rfc7519#section-4.1.3
+	Audience ClaimStrings `json:"aud,omitempty"`
+
+	// the `exp` (Expiration Time) claim. See https://datatracker.ietf.org/doc/html/rfc7519#section-4.1.4
+	ExpiresAt *NumericDate `json:"exp,omitempty"`
+
+	// the `nbf` (Not Before) claim. See https://datatracker.ietf.org/doc/html/rfc7519#section-4.1.5
+	NotBefore *NumericDate `json:"nbf,omitempty"`
+
+	// the `iat` (Issued At) claim. See https://datatracker.ietf.org/doc/html/rfc7519#section-4.1.6
+	IssuedAt *NumericDate `json:"iat,omitempty"`
+
+	// the `jti` (JWT ID) claim. See https://datatracker.ietf.org/doc/html/rfc7519#section-4.1.7
+	ID string `json:"jti,omitempty"`
+}
+
+// GetExpirationTime implements the Claims interface.
+func (c RegisteredClaims) GetExpirationTime() (*NumericDate, error) {
+	return c.ExpiresAt, nil
+}
+
+// GetNotBefore implements the Claims interface.
+func (c RegisteredClaims) GetNotBefore() (*NumericDate, error) {
+	return c.NotBefore, nil
+}
+
+// GetIssuedAt implements the Claims interface.
+func (c RegisteredClaims) GetIssuedAt() (*NumericDate, error) {
+	return c.IssuedAt, nil
+}
+
+// GetAudience implements the Claims interface.
+func (c RegisteredClaims) GetAudience() (ClaimStrings, error) {
+	return c.Audience, nil
+}
+
+// GetIssuer implements the Claims interface.
+func (c RegisteredClaims) GetIssuer() (string, error) {
+	return c.Issuer, nil
+}
+
+// GetSubject implements the Claims interface.
+func (c RegisteredClaims) GetSubject() (string, error) {
+	return c.Subject, nil
+}

token.go

@@ -4,7 +4,6 @@ import (
 	"encoding/base64"
 	"encoding/json"
 	"strings"
-	"time"
 )
 
 // DecodePaddingAllowed will switch the codec used for decoding JWTs respectively. Note that the JWS RFC7515
@@ -20,11 +19,6 @@ var DecodePaddingAllowed bool
 // To use strict decoding, set this boolean to `true` prior to using this package.
 var DecodeStrict bool
 
-// TimeFunc provides the current time when parsing token to validate "exp" claim (expiration time).
-// You can override it to use another time value.  This is useful for testing or if your
-// server uses a different time zone than your tokens.
-var TimeFunc = time.Now
-
 // Keyfunc will be used by the Parse methods as a callback function to supply
 // the key for verification.  The function receives the parsed,
 // but unverified Token.  This allows you to use properties in the

validator.go

@@ -0,0 +1,264 @@
+package jwt
+
+import (
+	"crypto/subtle"
+	"time"
+)
+
+// validator is the core of the new Validation API. It is automatically used by
+// a [Parser] during parsing and can be modified with various parser options.
+//
+// Note: This struct is intentionally not exported (yet) as we want to
+// internally finalize its API. In the future, we might make it publicly available.
+type validator struct {
+	// leeway is an optional leeway that can be provided to account for clock skew.
+	leeway time.Duration
+
+	// timeFunc is used to supply the current time that is needed for
+	// validation. If unspecified, this defaults to time.Now.
+	timeFunc func() time.Time
+
+	// verifyIat specifies whether the iat (Issued At) claim will be verified.
+	// According to https://www.rfc-editor.org/rfc/rfc7519#section-4.1.6 this
+	// only specifies the age of the token, but no validation check is
+	// necessary. However, if wanted, it can be checked if the iat is
+	// unrealistic, i.e., in the future.
+	verifyIat bool
+
+	// expectedAud contains the audience this token expects. Supplying an empty
+	// string will disable aud checking.
+	expectedAud string
+
+	// expectedIss contains the issuer this token expects. Supplying an empty
+	// string will disable iss checking.
+	expectedIss string
+
+	// expectedSub contains the subject this token expects. Supplying an empty
+	// string will disable sub checking.
+	expectedSub string
+}
+
+// CustomClaims represents a custom claims interface, which can be built upon the integrated
+// claim types, such as map claims or registered claims.
+type CustomClaims interface {
+	// CustomValidation can be implemented by a user-specific claim to support
+	// additional validation steps in addition to the regular validation.
+	CustomValidation() error
+}
+
+// newValidator can be used to create a stand-alone validator with the supplied
+// options. This validator can then be used to validate already parsed claims.
+func newValidator(opts ...ParserOption) *validator {
+	p := NewParser(opts...)
+	return p.validator
+}
+
+// Validate validates the given claims. It will also perform any custom validation if claims implements the CustomValidator interface.
+func (v *validator) Validate(claims Claims) error {
+	var now time.Time
+	vErr := new(ValidationError)
+
+	// Check, if we have a time func
+	if v.timeFunc != nil {
+		now = v.timeFunc()
+	} else {
+		now = time.Now()
+	}
+
+	// We always need to check the expiration time, but the claim itself is OPTIONAL
+	if !v.VerifyExpiresAt(claims, now, false) {
+		vErr.Inner = ErrTokenExpired
+		vErr.Errors |= ValidationErrorExpired
+	}
+
+	// We always need to check not-before, but the claim itself is OPTIONAL
+	if !v.VerifyNotBefore(claims, now, false) {
+		vErr.Inner = ErrTokenNotValidYet
+		vErr.Errors |= ValidationErrorNotValidYet
+	}
+
+	// Check issued-at if the option is enabled
+	if v.verifyIat && !v.VerifyIssuedAt(claims, now, false) {
+		vErr.Inner = ErrTokenUsedBeforeIssued
+		vErr.Errors |= ValidationErrorIssuedAt
+	}
+
+	// If we have an expected audience, we also require the audience claim
+	if v.expectedAud != "" && !v.VerifyAudience(claims, v.expectedAud, true) {
+		vErr.Inner = ErrTokenInvalidAudience
+		vErr.Errors |= ValidationErrorAudience
+	}
+
+	// If we have an expected issuer, we also require the issuer claim
+	if v.expectedIss != "" && !v.VerifyIssuer(claims, v.expectedIss, true) {
+		vErr.Inner = ErrTokenInvalidIssuer
+		vErr.Errors |= ValidationErrorIssuer
+	}
+
+	// If we have an expected subject, we also require the subject claim
+	if v.expectedSub != "" && !v.VerifySubject(claims, v.expectedSub, true) {
+		vErr.Inner = ErrTokenInvalidSubject
+		vErr.Errors |= ValidationErrorSubject
+	}
+
+	// Finally, we want to give the claim itself some possibility to do some
+	// additional custom validation based on their custom claims
+	cvt, ok := claims.(CustomClaims)
+	if ok {
+		if err := cvt.CustomValidation(); err != nil {
+			vErr.Inner = err
+			vErr.Errors |= ValidationErrorClaimsInvalid
+		}
+	}
+
+	if vErr.valid() {
+		return nil
+	}
+
+	return vErr
+}
+
+// VerifyAudience compares the aud claim against cmp.
+// If required is false, this method will return true if the value matches or is unset
+func (v *validator) VerifyAudience(claims Claims, cmp string, req bool) bool {
+	aud, err := claims.GetAudience()
+	if err != nil {
+		return false
+	}
+
+	return verifyAud(aud, cmp, req)
+}
+
+// VerifyExpiresAt compares the exp claim against cmp (cmp < exp).
+// If req is false, it will return true, if exp is unset.
+func (v *validator) VerifyExpiresAt(claims Claims, cmp time.Time, req bool) bool {
+	var time *time.Time = nil
+
+	exp, err := claims.GetExpirationTime()
+	if err != nil {
+		return false
+	} else if exp != nil {
+		time = &exp.Time
+	}
+
+	return verifyExp(time, cmp, req, v.leeway)
+}
+
+// VerifyIssuedAt compares the iat claim against cmp (cmp >= iat).
+// If req is false, it will return true, if iat is unset.
+func (v *validator) VerifyIssuedAt(claims Claims, cmp time.Time, req bool) bool {
+	var time *time.Time = nil
+
+	iat, err := claims.GetIssuedAt()
+	if err != nil {
+		return false
+	} else if iat != nil {
+		time = &iat.Time
+	}
+
+	return verifyIat(time, cmp, req, v.leeway)
+}
+
+// VerifyNotBefore compares the nbf claim against cmp (cmp >= nbf).
+// If req is false, it will return true, if nbf is unset.
+func (v *validator) VerifyNotBefore(claims Claims, cmp time.Time, req bool) bool {
+	var time *time.Time = nil
+
+	nbf, err := claims.GetNotBefore()
+	if err != nil {
+		return false
+	} else if nbf != nil {
+		time = &nbf.Time
+	}
+
+	return verifyNbf(time, cmp, req, v.leeway)
+}
+
+// VerifyIssuer compares the iss claim against cmp.
+// If required is false, this method will return true if the value matches or is unset
+func (v *validator) VerifyIssuer(claims Claims, cmp string, req bool) bool {
+	iss, err := claims.GetIssuer()
+	if err != nil {
+		return false
+	}
+
+	return verifyIss(iss, cmp, req)
+}
+
+// VerifySubject compares the sub claim against cmp.
+// If required is false, this method will return true if the value matches or is unset
+func (v *validator) VerifySubject(claims Claims, cmp string, req bool) bool {
+	iss, err := claims.GetSubject()
+	if err != nil {
+		return false
+	}
+
+	return verifySub(iss, cmp, req)
+}
+
+// ----- helpers
+
+func verifyAud(aud []string, cmp string, required bool) bool {
+	if len(aud) == 0 {
+		return !required
+	}
+	// use a var here to keep constant time compare when looping over a number of claims
+	result := false
+
+	var stringClaims string
+	for _, a := range aud {
+		if subtle.ConstantTimeCompare([]byte(a), []byte(cmp)) != 0 {
+			result = true
+		}
+		stringClaims = stringClaims + a
+	}
+
+	// case where "" is sent in one or many aud claims
+	if stringClaims == "" {
+		return !required
+	}
+
+	return result
+}
+
+func verifyExp(exp *time.Time, now time.Time, required bool, skew time.Duration) bool {
+	if exp == nil {
+		return !required
+	}
+
+	return now.Before((*exp).Add(+skew))
+}
+
+func verifyIat(iat *time.Time, now time.Time, required bool, skew time.Duration) bool {
+	if iat == nil {
+		return !required
+	}
+
+	t := iat.Add(-skew)
+	return !now.Before(t)
+}
+
+func verifyNbf(nbf *time.Time, now time.Time, required bool, skew time.Duration) bool {
+	if nbf == nil {
+		return !required
+	}
+
+	t := nbf.Add(-skew)
+	return !now.Before(t)
+}
+
+func verifyIss(iss string, cmp string, required bool) bool {
+	if iss == "" {
+		return !required
+	}
+
+	return iss == cmp
+}
+
+func verifySub(sub string, cmp string, required bool) bool {
+	if sub == "" {
+		return !required
+	}
+
+	return sub == cmp
+}