diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index cea5f11..9840fff 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -25,7 +25,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        go: [1.17, 1.18, 1.19]
+        go: ["1.18", "1.19", "1.20"]
     steps:
       - name: Checkout
         uses: actions/checkout@v3
diff --git a/errors.go b/errors.go
index a63827f..23bb616 100644
--- a/errors.go
+++ b/errors.go
@@ -2,120 +2,48 @@ package jwt
 
 import (
 	"errors"
+	"strings"
 )
 
-// Error constants
 var (
-	ErrInvalidKey      = errors.New("key is invalid")
-	ErrInvalidKeyType  = errors.New("key is of invalid type")
-	ErrHashUnavailable = errors.New("the requested hash function is unavailable")
-
-	ErrTokenMalformed        = errors.New("token is malformed")
-	ErrTokenUnverifiable     = errors.New("token is unverifiable")
-	ErrTokenSignatureInvalid = errors.New("token signature is invalid")
-
-	ErrTokenInvalidAudience  = errors.New("token has invalid audience")
-	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")
-
-	ErrInvalidType = errors.New("invalid type for claim")
+	ErrInvalidKey                = errors.New("key is invalid")
+	ErrInvalidKeyType            = errors.New("key is of invalid type")
+	ErrHashUnavailable           = errors.New("the requested hash function is unavailable")
+	ErrTokenMalformed            = errors.New("token is malformed")
+	ErrTokenUnverifiable         = errors.New("token is unverifiable")
+	ErrTokenSignatureInvalid     = errors.New("token signature is invalid")
+	ErrTokenRequiredClaimMissing = errors.New("token is missing required claim")
+	ErrTokenInvalidAudience      = errors.New("token has invalid audience")
+	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")
+	ErrInvalidType               = errors.New("invalid type for claim")
 )
 
-// The errors that might occur when parsing and validating a token
-const (
-	ValidationErrorMalformed        uint32 = 1 << iota // Token is malformed
-	ValidationErrorUnverifiable                        // Token could not be verified because of signing problems
-	ValidationErrorSignatureInvalid                    // Signature validation failed
-
-	// 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
-)
-
-// NewValidationError is a helper for constructing a ValidationError with a string error message
-func NewValidationError(errorText string, errorFlags uint32) *ValidationError {
-	return &ValidationError{
-		text:   errorText,
-		Errors: errorFlags,
-	}
+// joinedError is an error type that works similar to what [errors.Join]
+// produces, with the exception that it has a nice error string; mainly its
+// error messages are concatenated using a comma, rather than a newline.
+type joinedError struct {
+	errs []error
 }
 
-// ValidationError represents an error from Parse if token is not valid
-type ValidationError struct {
-	// Inner stores the error returned by external dependencies, e.g.: KeyFunc
-	Inner error
-	// Errors is a bit-field. See ValidationError... constants
-	Errors uint32
-	// Text can be used for errors that do not have a valid error just have text
-	text string
-}
-
-// Error is the implementation of the err interface.
-func (e ValidationError) Error() string {
-	if e.Inner != nil {
-		return e.Inner.Error()
-	} else if e.text != "" {
-		return e.text
-	} else {
-		return "token is invalid"
-	}
-}
-
-// Unwrap gives errors.Is and errors.As access to the inner error.
-func (e *ValidationError) Unwrap() error {
-	return e.Inner
-}
-
-// No errors
-func (e *ValidationError) valid() bool {
-	return e.Errors == 0
-}
-
-// Is checks if this ValidationError is of the supplied error. We are first
-// checking for the exact error message by comparing the inner error message. If
-// that fails, we compare using the error flags. This way we can use custom
-// error messages (mainly for backwards compatibility) and still leverage
-// errors.Is using the global error variables.
-func (e *ValidationError) Is(err error) bool {
-	// Check, if our inner error is a direct match
-	if errors.Is(errors.Unwrap(e), err) {
-		return true
+func (je joinedError) Error() string {
+	msg := []string{}
+	for _, err := range je.errs {
+		msg = append(msg, err.Error())
 	}
 
-	// Otherwise, we need to match using our error flags
-	switch err {
-	case ErrTokenMalformed:
-		return e.Errors&ValidationErrorMalformed != 0
-	case ErrTokenUnverifiable:
-		return e.Errors&ValidationErrorUnverifiable != 0
-	case ErrTokenSignatureInvalid:
-		return e.Errors&ValidationErrorSignatureInvalid != 0
-	case ErrTokenInvalidAudience:
-		return e.Errors&ValidationErrorAudience != 0
-	case ErrTokenExpired:
-		return e.Errors&ValidationErrorExpired != 0
-	case ErrTokenUsedBeforeIssued:
-		return e.Errors&ValidationErrorIssuedAt != 0
-	case ErrTokenInvalidIssuer:
-		return e.Errors&ValidationErrorIssuer != 0
-	case ErrTokenNotValidYet:
-		return e.Errors&ValidationErrorNotValidYet != 0
-	case ErrTokenInvalidId:
-		return e.Errors&ValidationErrorId != 0
-	case ErrTokenInvalidClaims:
-		return e.Errors&ValidationErrorClaimsInvalid != 0
-	}
-
-	return false
+	return strings.Join(msg, ", ")
+}
+
+// joinErrors joins together multiple errors. Useful for scenarios where
+// multiple errors next to each other occur, e.g., in claims validation.
+func joinErrors(errs ...error) error {
+	return &joinedError{
+		errs: errs,
+	}
 }
diff --git a/errors_go1_20.go b/errors_go1_20.go
new file mode 100644
index 0000000..a893d35
--- /dev/null
+++ b/errors_go1_20.go
@@ -0,0 +1,47 @@
+//go:build go1.20
+// +build go1.20
+
+package jwt
+
+import (
+	"fmt"
+)
+
+// Unwrap implements the multiple error unwrapping for this error type, which is
+// possible in Go 1.20.
+func (je joinedError) Unwrap() []error {
+	return je.errs
+}
+
+// newError creates a new error message with a detailed error message. The
+// message will be prefixed with the contents of the supplied error type.
+// Additionally, more errors, that provide more context can be supplied which
+// will be appended to the message. This makes use of Go 1.20's possibility to
+// include more than one %w formatting directive in [fmt.Errorf].
+//
+// For example,
+//
+//	newError("no keyfunc was provided", ErrTokenUnverifiable)
+//
+// will produce the error string
+//
+//	"token is unverifiable: no keyfunc was provided"
+func newError(message string, err error, more ...error) error {
+	var format string
+	var args []any
+	if message != "" {
+		format = "%w: %s"
+		args = []any{err, message}
+	} else {
+		format = "%w"
+		args = []any{err}
+	}
+
+	for _, e := range more {
+		format += ": %w"
+		args = append(args, e)
+	}
+
+	err = fmt.Errorf(format, args...)
+	return err
+}
diff --git a/errors_go_other.go b/errors_go_other.go
new file mode 100644
index 0000000..3afb04e
--- /dev/null
+++ b/errors_go_other.go
@@ -0,0 +1,78 @@
+//go:build !go1.20
+// +build !go1.20
+
+package jwt
+
+import (
+	"errors"
+	"fmt"
+)
+
+// Is implements checking for multiple errors using [errors.Is], since multiple
+// error unwrapping is not possible in versions less than Go 1.20.
+func (je joinedError) Is(err error) bool {
+	for _, e := range je.errs {
+		if errors.Is(e, err) {
+			return true
+		}
+	}
+
+	return false
+}
+
+// wrappedErrors is a workaround for wrapping multiple errors in environments
+// where Go 1.20 is not available. It basically uses the already implemented
+// functionatlity of joinedError to handle multiple errors with supplies a
+// custom error message that is identical to the one we produce in Go 1.20 using
+// multiple %w directives.
+type wrappedErrors struct {
+	msg string
+	joinedError
+}
+
+// Error returns the stored error string
+func (we wrappedErrors) Error() string {
+	return we.msg
+}
+
+// newError creates a new error message with a detailed error message. The
+// message will be prefixed with the contents of the supplied error type.
+// Additionally, more errors, that provide more context can be supplied which
+// will be appended to the message. Since we cannot use of Go 1.20's possibility
+// to include more than one %w formatting directive in [fmt.Errorf], we have to
+// emulate that.
+//
+// For example,
+//
+//	newError("no keyfunc was provided", ErrTokenUnverifiable)
+//
+// will produce the error string
+//
+//	"token is unverifiable: no keyfunc was provided"
+func newError(message string, err error, more ...error) error {
+	// We cannot wrap multiple errors here with %w, so we have to be a little
+	// bit creative. Basically, we are using %s instead of %w to produce the
+	// same error message and then throw the result into a custom error struct.
+	var format string
+	var args []any
+	if message != "" {
+		format = "%s: %s"
+		args = []any{err, message}
+	} else {
+		format = "%s"
+		args = []any{err}
+	}
+	errs := []error{err}
+
+	for _, e := range more {
+		format += ": %s"
+		args = append(args, e)
+		errs = append(errs, e)
+	}
+
+	err = &wrappedErrors{
+		msg:         fmt.Sprintf(format, args...),
+		joinedError: joinedError{errs: errs},
+	}
+	return err
+}
diff --git a/errors_test.go b/errors_test.go
new file mode 100644
index 0000000..fd4004b
--- /dev/null
+++ b/errors_test.go
@@ -0,0 +1,95 @@
+package jwt
+
+import (
+	"errors"
+	"io"
+	"testing"
+)
+
+func Test_joinErrors(t *testing.T) {
+	type args struct {
+		errs []error
+	}
+	tests := []struct {
+		name        string
+		args        args
+		wantErrors  []error
+		wantMessage string
+	}{
+		{
+			name: "multiple errors",
+			args: args{
+				errs: []error{ErrTokenNotValidYet, ErrTokenExpired},
+			},
+			wantErrors:  []error{ErrTokenNotValidYet, ErrTokenExpired},
+			wantMessage: "token is not valid yet, token is expired",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			err := joinErrors(tt.args.errs...)
+			for _, wantErr := range tt.wantErrors {
+				if !errors.Is(err, wantErr) {
+					t.Errorf("joinErrors() error = %v, does not contain %v", err, wantErr)
+				}
+			}
+
+			if err.Error() != tt.wantMessage {
+				t.Errorf("joinErrors() error.Error() = %v, wantMessage %v", err, tt.wantMessage)
+			}
+		})
+	}
+}
+
+func Test_newError(t *testing.T) {
+	type args struct {
+		message string
+		err     error
+		more    []error
+	}
+	tests := []struct {
+		name        string
+		args        args
+		wantErrors  []error
+		wantMessage string
+	}{
+		{
+			name:        "single error",
+			args:        args{message: "something is wrong", err: ErrTokenMalformed},
+			wantMessage: "token is malformed: something is wrong",
+			wantErrors:  []error{ErrTokenMalformed},
+		},
+		{
+			name:        "two errors",
+			args:        args{message: "something is wrong", err: ErrTokenMalformed, more: []error{io.ErrUnexpectedEOF}},
+			wantMessage: "token is malformed: something is wrong: unexpected EOF",
+			wantErrors:  []error{ErrTokenMalformed},
+		},
+		{
+			name:        "two errors, no detail",
+			args:        args{message: "", err: ErrTokenInvalidClaims, more: []error{ErrTokenExpired}},
+			wantMessage: "token has invalid claims: token is expired",
+			wantErrors:  []error{ErrTokenInvalidClaims, ErrTokenExpired},
+		},
+		{
+			name:        "two errors, no detail and join error",
+			args:        args{message: "", err: ErrTokenInvalidClaims, more: []error{joinErrors(ErrTokenExpired, ErrTokenNotValidYet)}},
+			wantMessage: "token has invalid claims: token is expired, token is not valid yet",
+			wantErrors:  []error{ErrTokenInvalidClaims, ErrTokenExpired, ErrTokenNotValidYet},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			err := newError(tt.args.message, tt.args.err, tt.args.more...)
+			for _, wantErr := range tt.wantErrors {
+				if !errors.Is(err, wantErr) {
+					t.Errorf("newError() error = %v, does not contain %v", err, wantErr)
+				}
+			}
+
+			if err.Error() != tt.wantMessage {
+				t.Errorf("newError() error.Error() = %v, wantMessage %v", err, tt.wantMessage)
+			}
+		})
+	}
+}
diff --git a/go.mod b/go.mod
index 3b8690b..7fbfced 100644
--- a/go.mod
+++ b/go.mod
@@ -1,3 +1,3 @@
 module github.com/golang-jwt/jwt/v5
 
-go 1.16
+go 1.18
diff --git a/map_claims.go b/map_claims.go
index 43c17a4..b2b51a1 100644
--- a/map_claims.go
+++ b/map_claims.go
@@ -2,6 +2,7 @@ package jwt
 
 import (
 	"encoding/json"
+	"fmt"
 )
 
 // MapClaims is a claims type that uses the map[string]interface{} for JSON
@@ -60,7 +61,7 @@ func (m MapClaims) parseNumericDate(key string) (*NumericDate, error) {
 		return newNumericDateFromSeconds(v), nil
 	}
 
-	return nil, ErrInvalidType
+	return nil, newError(fmt.Sprintf("%s is invalid", key), ErrInvalidType)
 }
 
 // parseClaimsString tries to parse a key in the map claims type as a
@@ -76,7 +77,7 @@ func (m MapClaims) parseClaimsString(key string) (ClaimStrings, error) {
 		for _, a := range v {
 			vs, ok := a.(string)
 			if !ok {
-				return nil, ErrInvalidType
+				return nil, newError(fmt.Sprintf("%s is invalid", key), ErrInvalidType)
 			}
 			cs = append(cs, vs)
 		}
@@ -101,7 +102,7 @@ func (m MapClaims) parseString(key string) (string, error) {
 
 	iss, ok = raw.(string)
 	if !ok {
-		return "", ErrInvalidType
+		return "", newError(fmt.Sprintf("%s is invalid", key), ErrInvalidType)
 	}
 
 	return iss, nil
diff --git a/none.go b/none.go
index f19835d..a16495a 100644
--- a/none.go
+++ b/none.go
@@ -13,7 +13,7 @@ type unsafeNoneMagicConstant string
 
 func init() {
 	SigningMethodNone = &signingMethodNone{}
-	NoneSignatureTypeDisallowedError = NewValidationError("'none' signature type is not allowed", ValidationErrorSignatureInvalid)
+	NoneSignatureTypeDisallowedError = newError("'none' signature type is not allowed", ErrTokenUnverifiable)
 
 	RegisterSigningMethod(SigningMethodNone.Alg(), func() SigningMethod {
 		return SigningMethodNone
@@ -33,10 +33,7 @@ func (m *signingMethodNone) Verify(signingString, signature string, key interfac
 	}
 	// If signing method is none, signature must be an empty string
 	if signature != "" {
-		return NewValidationError(
-			"'none' signing method with non-empty signature",
-			ValidationErrorSignatureInvalid,
-		)
+		return newError("'none' signing method with non-empty signature", ErrTokenUnverifiable)
 	}
 
 	// Accept 'none' signing method.
diff --git a/parser.go b/parser.go
index b9c3ffb..46b6793 100644
--- a/parser.go
+++ b/parser.go
@@ -65,7 +65,7 @@ func (p *Parser) ParseWithClaims(tokenString string, claims Claims, keyFunc Keyf
 		}
 		if !signingMethodValid {
 			// signing method is not in the listed set
-			return token, NewValidationError(fmt.Sprintf("signing method %v is invalid", alg), ValidationErrorSignatureInvalid)
+			return token, newError(fmt.Sprintf("signing method %v is invalid", alg), ErrTokenSignatureInvalid)
 		}
 	}
 
@@ -73,17 +73,17 @@ func (p *Parser) ParseWithClaims(tokenString string, claims Claims, keyFunc Keyf
 	var key interface{}
 	if keyFunc == nil {
 		// keyFunc was not provided.  short circuiting validation
-		return token, NewValidationError("no Keyfunc was provided.", ValidationErrorUnverifiable)
+		return token, newError("no keyfunc was provided", ErrTokenUnverifiable)
 	}
 	if key, err = keyFunc(token); err != nil {
-		// keyFunc returned an error
-		if ve, ok := err.(*ValidationError); ok {
-			return token, ve
-		}
-		return token, &ValidationError{Inner: err, Errors: ValidationErrorUnverifiable}
+		return token, newError("error while executing keyfunc", ErrTokenUnverifiable, err)
 	}
 
-	vErr := &ValidationError{}
+	// Perform signature validation
+	token.Signature = parts[2]
+	if err = token.Method.Verify(strings.Join(parts[0:2], "."), token.Signature, key); err != nil {
+		return token, newError("", ErrTokenSignatureInvalid, err)
+	}
 
 	// Validate Claims
 	if !p.skipClaimsValidation {
@@ -93,29 +93,14 @@ func (p *Parser) ParseWithClaims(tokenString string, claims Claims, keyFunc Keyf
 		}
 
 		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 {
-				vErr = &ValidationError{Inner: err, Errors: ValidationErrorClaimsInvalid}
-			} else {
-				vErr = e
-			}
+			return token, newError("", ErrTokenInvalidClaims, err)
 		}
 	}
 
-	// Perform validation
-	token.Signature = parts[2]
-	if err = token.Method.Verify(strings.Join(parts[0:2], "."), token.Signature, key); err != nil {
-		vErr.Inner = err
-		vErr.Errors |= ValidationErrorSignatureInvalid
-	}
+	// No errors so far, token is valid.
+	token.Valid = true
 
-	if vErr.valid() {
-		token.Valid = true
-		return token, nil
-	}
-
-	return token, vErr
+	return token, nil
 }
 
 // ParseUnverified parses the token but doesn't validate the signature.
@@ -127,7 +112,7 @@ func (p *Parser) ParseWithClaims(tokenString string, claims Claims, keyFunc Keyf
 func (p *Parser) ParseUnverified(tokenString string, claims Claims) (token *Token, parts []string, err error) {
 	parts = strings.Split(tokenString, ".")
 	if len(parts) != 3 {
-		return nil, parts, NewValidationError("token contains an invalid number of segments", ValidationErrorMalformed)
+		return nil, parts, newError("token contains an invalid number of segments", ErrTokenMalformed)
 	}
 
 	token = &Token{Raw: tokenString}
@@ -136,12 +121,12 @@ func (p *Parser) ParseUnverified(tokenString string, claims Claims) (token *Toke
 	var headerBytes []byte
 	if headerBytes, err = DecodeSegment(parts[0]); err != nil {
 		if strings.HasPrefix(strings.ToLower(tokenString), "bearer ") {
-			return token, parts, NewValidationError("tokenstring should not contain 'bearer '", ValidationErrorMalformed)
+			return token, parts, newError("tokenstring should not contain 'bearer '", ErrTokenMalformed)
 		}
-		return token, parts, &ValidationError{Inner: err, Errors: ValidationErrorMalformed}
+		return token, parts, newError("could not base64 decode header", ErrTokenMalformed, err)
 	}
 	if err = json.Unmarshal(headerBytes, &token.Header); err != nil {
-		return token, parts, &ValidationError{Inner: err, Errors: ValidationErrorMalformed}
+		return token, parts, newError("could not JSON decode header", ErrTokenMalformed, err)
 	}
 
 	// parse Claims
@@ -149,7 +134,7 @@ func (p *Parser) ParseUnverified(tokenString string, claims Claims) (token *Toke
 	token.Claims = claims
 
 	if claimBytes, err = DecodeSegment(parts[1]); err != nil {
-		return token, parts, &ValidationError{Inner: err, Errors: ValidationErrorMalformed}
+		return token, parts, newError("could not base64 decode claim", ErrTokenMalformed, err)
 	}
 	dec := json.NewDecoder(bytes.NewBuffer(claimBytes))
 	if p.useJSONNumber {
@@ -163,16 +148,16 @@ func (p *Parser) ParseUnverified(tokenString string, claims Claims) (token *Toke
 	}
 	// Handle decode error
 	if err != nil {
-		return token, parts, &ValidationError{Inner: err, Errors: ValidationErrorMalformed}
+		return token, parts, newError("could not JSON decode claim", ErrTokenMalformed, err)
 	}
 
 	// Lookup signature method
 	if method, ok := token.Header["alg"].(string); ok {
 		if token.Method = GetSigningMethod(method); token.Method == nil {
-			return token, parts, NewValidationError("signing method (alg) is unavailable.", ValidationErrorUnverifiable)
+			return token, parts, newError("signing method (alg) is unavailable", ErrTokenUnverifiable)
 		}
 	} else {
-		return token, parts, NewValidationError("signing method (alg) is unspecified.", ValidationErrorUnverifiable)
+		return token, parts, newError("signing method (alg) is unspecified", ErrTokenUnverifiable)
 	}
 
 	return token, parts, nil
diff --git a/parser_test.go b/parser_test.go
index 306f8b5..fdb5eef 100644
--- a/parser_test.go
+++ b/parser_test.go
@@ -51,7 +51,6 @@ var jwtTestData = []struct {
 	keyfunc       jwt.Keyfunc
 	claims        jwt.Claims
 	valid         bool
-	errors        uint32
 	err           []error
 	parser        *jwt.Parser
 	signingMethod jwt.SigningMethod // The method to sign the JWT token for test purpose
@@ -62,7 +61,16 @@ var jwtTestData = []struct {
 		defaultKeyFunc,
 		nil,
 		false,
-		jwt.ValidationErrorMalformed,
+		[]error{jwt.ErrTokenMalformed},
+		nil,
+		jwt.SigningMethodRS256,
+	},
+	{
+		"invalid JSON claim",
+		"eyJhbGciOiJSUzI1NiIsInppcCI6IkRFRiJ9.eNqqVkqtKFCyMjQ1s7Q0sbA0MtFRyk3NTUot8kxRslIKLbZQggn4JeamAoUcfRz99HxcXRWeze172tr4bFq7Ui0AAAD__w.jBXD4LT4aq4oXTgDoPkiV6n4QdSZPZI1Z4J8MWQC42aHK0oXwcovEU06dVbtB81TF-2byuu0-qi8J0GUttODT67k6gCl6DV_iuCOV7gczwTcvKslotUvXzoJ2wa0QuujnjxLEE50r0p6k0tsv_9OIFSUZzDksJFYNPlJH2eFG55DROx4TsOz98az37SujZi9GGbTc9SLgzFHPrHMrovRZ5qLC_w4JrdtsLzBBI11OQJgRYwV8fQf4O8IsMkHtetjkN7dKgUkJtRarNWOk76rpTPppLypiLU4_J0-wrElLMh1TzUVZW6Fz2cDHDDBACJgMmKQ2pOFEDK_vYZN74dLCF5GiTZV6DbXhNxO7lqT7JUN4a3p2z96G7WNRjblf2qZeuYdQvkIsiK-rCbSIE836XeY5gaBgkOzuEvzl_tMrpRmb5Oox1ibOfVT2KBh9Lvqsb1XbQjCio2CLE2ViCLqoe0AaRqlUyrk3n8BIG-r0IW4dcw96CEryEMIjsjVp9mtPXamJzf391kt8Rf3iRBqwv3zP7Plg1ResXbmsFUgOflAUPcYmfLug4W3W52ntcUlTHAKXrNfaJL9QQiYAaDukG-ZHDytsOWTuuXw7lVxjt-XYi1VbRAIjh1aIYSELEmEpE4Ny74htQtywYXMQNfJpB0nNn8IiWakgcYYMJ0TmKM",
+		defaultKeyFunc,
+		nil,
+		false,
 		[]error{jwt.ErrTokenMalformed},
 		nil,
 		jwt.SigningMethodRS256,
@@ -73,7 +81,6 @@ var jwtTestData = []struct {
 		defaultKeyFunc,
 		nil,
 		false,
-		jwt.ValidationErrorMalformed,
 		[]error{jwt.ErrTokenMalformed},
 		nil,
 		jwt.SigningMethodRS256,
@@ -84,7 +91,6 @@ var jwtTestData = []struct {
 		defaultKeyFunc,
 		jwt.MapClaims{"foo": "bar"},
 		true,
-		0,
 		nil,
 		nil,
 		jwt.SigningMethodRS256,
@@ -95,7 +101,6 @@ var jwtTestData = []struct {
 		defaultKeyFunc,
 		jwt.MapClaims{"foo": "bar", "exp": float64(time.Now().Unix() - 100)},
 		false,
-		jwt.ValidationErrorExpired,
 		[]error{jwt.ErrTokenExpired},
 		nil,
 		jwt.SigningMethodRS256,
@@ -106,7 +111,6 @@ var jwtTestData = []struct {
 		defaultKeyFunc,
 		jwt.MapClaims{"foo": "bar", "nbf": float64(time.Now().Unix() + 100)},
 		false,
-		jwt.ValidationErrorNotValidYet,
 		[]error{jwt.ErrTokenNotValidYet},
 		nil,
 		jwt.SigningMethodRS256,
@@ -117,8 +121,7 @@ var jwtTestData = []struct {
 		defaultKeyFunc,
 		jwt.MapClaims{"foo": "bar", "nbf": float64(time.Now().Unix() + 100), "exp": float64(time.Now().Unix() - 100)},
 		false,
-		jwt.ValidationErrorNotValidYet | jwt.ValidationErrorExpired,
-		[]error{jwt.ErrTokenNotValidYet},
+		[]error{jwt.ErrTokenNotValidYet, jwt.ErrTokenExpired},
 		nil,
 		jwt.SigningMethodRS256,
 	},
@@ -128,7 +131,6 @@ var jwtTestData = []struct {
 		defaultKeyFunc,
 		jwt.MapClaims{"foo": "bar"},
 		false,
-		jwt.ValidationErrorSignatureInvalid,
 		[]error{jwt.ErrTokenSignatureInvalid, rsa.ErrVerification},
 		nil,
 		jwt.SigningMethodRS256,
@@ -139,7 +141,6 @@ var jwtTestData = []struct {
 		nilKeyFunc,
 		jwt.MapClaims{"foo": "bar"},
 		false,
-		jwt.ValidationErrorUnverifiable,
 		[]error{jwt.ErrTokenUnverifiable},
 		nil,
 		jwt.SigningMethodRS256,
@@ -150,7 +151,6 @@ var jwtTestData = []struct {
 		emptyKeyFunc,
 		jwt.MapClaims{"foo": "bar"},
 		false,
-		jwt.ValidationErrorSignatureInvalid,
 		[]error{jwt.ErrTokenSignatureInvalid},
 		nil,
 		jwt.SigningMethodRS256,
@@ -161,7 +161,6 @@ var jwtTestData = []struct {
 		errorKeyFunc,
 		jwt.MapClaims{"foo": "bar"},
 		false,
-		jwt.ValidationErrorUnverifiable,
 		[]error{jwt.ErrTokenUnverifiable, errKeyFuncError},
 		nil,
 		jwt.SigningMethodRS256,
@@ -172,7 +171,6 @@ var jwtTestData = []struct {
 		defaultKeyFunc,
 		jwt.MapClaims{"foo": "bar"},
 		false,
-		jwt.ValidationErrorSignatureInvalid,
 		[]error{jwt.ErrTokenSignatureInvalid},
 		jwt.NewParser(jwt.WithValidMethods([]string{"HS256"})),
 		jwt.SigningMethodRS256,
@@ -183,7 +181,6 @@ var jwtTestData = []struct {
 		defaultKeyFunc,
 		jwt.MapClaims{"foo": "bar"},
 		true,
-		0,
 		nil,
 		jwt.NewParser(jwt.WithValidMethods([]string{"RS256", "HS256"})),
 		jwt.SigningMethodRS256,
@@ -194,7 +191,6 @@ var jwtTestData = []struct {
 		ecdsaKeyFunc,
 		jwt.MapClaims{"foo": "bar"},
 		false,
-		jwt.ValidationErrorSignatureInvalid,
 		[]error{jwt.ErrTokenSignatureInvalid},
 		jwt.NewParser(jwt.WithValidMethods([]string{"RS256", "HS256"})),
 		jwt.SigningMethodES256,
@@ -205,7 +201,6 @@ var jwtTestData = []struct {
 		ecdsaKeyFunc,
 		jwt.MapClaims{"foo": "bar"},
 		true,
-		0,
 		nil,
 		jwt.NewParser(jwt.WithValidMethods([]string{"HS256", "ES256"})),
 		jwt.SigningMethodES256,
@@ -216,7 +211,6 @@ var jwtTestData = []struct {
 		defaultKeyFunc,
 		jwt.MapClaims{"foo": json.Number("123.4")},
 		true,
-		0,
 		nil,
 		jwt.NewParser(jwt.WithJSONNumber()),
 		jwt.SigningMethodRS256,
@@ -227,7 +221,6 @@ var jwtTestData = []struct {
 		defaultKeyFunc,
 		jwt.MapClaims{"foo": "bar", "exp": json.Number(fmt.Sprintf("%v", time.Now().Unix()-100))},
 		false,
-		jwt.ValidationErrorExpired,
 		[]error{jwt.ErrTokenExpired},
 		jwt.NewParser(jwt.WithJSONNumber()),
 		jwt.SigningMethodRS256,
@@ -238,7 +231,6 @@ var jwtTestData = []struct {
 		defaultKeyFunc,
 		jwt.MapClaims{"foo": "bar", "nbf": json.Number(fmt.Sprintf("%v", time.Now().Unix()+100))},
 		false,
-		jwt.ValidationErrorNotValidYet,
 		[]error{jwt.ErrTokenNotValidYet},
 		jwt.NewParser(jwt.WithJSONNumber()),
 		jwt.SigningMethodRS256,
@@ -249,8 +241,7 @@ var jwtTestData = []struct {
 		defaultKeyFunc,
 		jwt.MapClaims{"foo": "bar", "nbf": json.Number(fmt.Sprintf("%v", time.Now().Unix()+100)), "exp": json.Number(fmt.Sprintf("%v", time.Now().Unix()-100))},
 		false,
-		jwt.ValidationErrorNotValidYet | jwt.ValidationErrorExpired,
-		[]error{jwt.ErrTokenNotValidYet},
+		[]error{jwt.ErrTokenNotValidYet, jwt.ErrTokenExpired},
 		jwt.NewParser(jwt.WithJSONNumber()),
 		jwt.SigningMethodRS256,
 	},
@@ -260,7 +251,6 @@ var jwtTestData = []struct {
 		defaultKeyFunc,
 		jwt.MapClaims{"foo": "bar", "nbf": json.Number(fmt.Sprintf("%v", time.Now().Unix()+100))},
 		true,
-		0,
 		nil,
 		jwt.NewParser(jwt.WithJSONNumber(), jwt.WithoutClaimsValidation()),
 		jwt.SigningMethodRS256,
@@ -273,7 +263,6 @@ var jwtTestData = []struct {
 			ExpiresAt: jwt.NewNumericDate(time.Now().Add(time.Second * 10)),
 		},
 		true,
-		0,
 		nil,
 		jwt.NewParser(jwt.WithJSONNumber()),
 		jwt.SigningMethodRS256,
@@ -286,7 +275,6 @@ var jwtTestData = []struct {
 			Audience: jwt.ClaimStrings{"test"},
 		},
 		true,
-		0,
 		nil,
 		jwt.NewParser(jwt.WithJSONNumber()),
 		jwt.SigningMethodRS256,
@@ -299,7 +287,6 @@ var jwtTestData = []struct {
 			Audience: jwt.ClaimStrings{"test", "test"},
 		},
 		true,
-		0,
 		nil,
 		jwt.NewParser(jwt.WithJSONNumber()),
 		jwt.SigningMethodRS256,
@@ -312,7 +299,6 @@ var jwtTestData = []struct {
 			Audience: nil, // because of the unmarshal error, this will be empty
 		},
 		false,
-		jwt.ValidationErrorMalformed,
 		[]error{jwt.ErrTokenMalformed},
 		jwt.NewParser(jwt.WithJSONNumber()),
 		jwt.SigningMethodRS256,
@@ -325,7 +311,6 @@ var jwtTestData = []struct {
 			Audience: nil, // because of the unmarshal error, this will be empty
 		},
 		false,
-		jwt.ValidationErrorMalformed,
 		[]error{jwt.ErrTokenMalformed},
 		jwt.NewParser(jwt.WithJSONNumber()),
 		jwt.SigningMethodRS256,
@@ -336,7 +321,6 @@ var jwtTestData = []struct {
 		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,
@@ -347,7 +331,6 @@ var jwtTestData = []struct {
 		defaultKeyFunc,
 		&jwt.RegisteredClaims{NotBefore: jwt.NewNumericDate(time.Now().Add(time.Second * 100))},
 		true,
-		0,
 		nil,
 		jwt.NewParser(jwt.WithLeeway(2 * time.Minute)),
 		jwt.SigningMethodRS256,
@@ -381,7 +364,6 @@ func TestParser_Parse(t *testing.T) {
 
 			// Parse the token
 			var token *jwt.Token
-			var ve *jwt.ValidationError
 			var err error
 			var parser = data.parser
 			if parser == nil {
@@ -417,23 +399,6 @@ func TestParser_Parse(t *testing.T) {
 				t.Errorf("[%v] Inconsistent behavior between returned error and token.Valid", data.name)
 			}
 
-			if data.errors != 0 {
-				if err == nil {
-					t.Errorf("[%v] Expecting error. Didn't get one.", data.name)
-				} else {
-					if errors.As(err, &ve) {
-						// compare the bitfield part of the error
-						if e := ve.Errors; e != data.errors {
-							t.Errorf("[%v] Errors don't match expectation.  %v != %v", data.name, e, data.errors)
-						}
-
-						if err.Error() == errKeyFuncError.Error() && ve.Inner != errKeyFuncError {
-							t.Errorf("[%v] Inner error does not match expectation.  %v != %v", data.name, ve.Inner, errKeyFuncError)
-						}
-					}
-				}
-			}
-
 			if data.err != nil {
 				if err == nil {
 					t.Errorf("[%v] Expecting error(s). Didn't get one.", data.name)
@@ -467,7 +432,7 @@ func TestParser_ParseUnverified(t *testing.T) {
 	// Iterate over test data set and run tests
 	for _, data := range jwtTestData {
 		// Skip test data, that intentionally contains malformed tokens, as they would lead to an error
-		if data.errors&jwt.ValidationErrorMalformed != 0 {
+		if len(data.err) == 1 && errors.Is(data.err[0], jwt.ErrTokenMalformed) {
 			continue
 		}
 
diff --git a/validator.go b/validator.go
index fa724c2..3850438 100644
--- a/validator.go
+++ b/validator.go
@@ -2,9 +2,32 @@ package jwt
 
 import (
 	"crypto/subtle"
+	"fmt"
 	"time"
 )
 
+// ClaimsValidator is an interface that can be implemented by custom claims who
+// wish to execute any additional claims validation based on
+// application-specific logic. The Validate function is then executed in
+// addition to the regular claims validation and any error returned is appended
+// to the final validation result.
+//
+//	type MyCustomClaims struct {
+//	    Foo string `json:"foo"`
+//	    jwt.RegisteredClaims
+//	}
+//
+//	func (m MyCustomClaims) Validate() error {
+//	    if m.Foo != "bar" {
+//	        return errors.New("must be foobar")
+//	    }
+//	    return nil
+//	}
+type ClaimsValidator interface {
+	Claims
+	Validate() error
+}
+
 // 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.
 //
@@ -47,10 +70,13 @@ func newValidator(opts ...ParserOption) *validator {
 }
 
 // Validate validates the given claims. It will also perform any custom
-// validation if claims implements the CustomValidator interface.
+// validation if claims implements the [ClaimsValidator] interface.
 func (v *validator) Validate(claims Claims) error {
-	var now time.Time
-	vErr := new(ValidationError)
+	var (
+		now  time.Time
+		errs []error = make([]error, 0, 6)
+		err  error
+	)
 
 	// Check, if we have a time func
 	if v.timeFunc != nil {
@@ -60,140 +86,139 @@ func (v *validator) Validate(claims Claims) error {
 	}
 
 	// We always need to check the expiration time, but usage of the claim
-	// itself is OPTIONAL
-	if !v.VerifyExpiresAt(claims, now, false) {
-		vErr.Inner = ErrTokenExpired
-		vErr.Errors |= ValidationErrorExpired
+	// itself is OPTIONAL.
+	if err = v.verifyExpiresAt(claims, now, false); err != nil {
+		errs = append(errs, err)
 	}
 
 	// We always need to check not-before, but usage of the claim itself is
-	// OPTIONAL
-	if !v.VerifyNotBefore(claims, now, false) {
-		vErr.Inner = ErrTokenNotValidYet
-		vErr.Errors |= ValidationErrorNotValidYet
+	// OPTIONAL.
+	if err = v.verifyNotBefore(claims, now, false); err != nil {
+		errs = append(errs, err)
 	}
 
 	// Check issued-at if the option is enabled
-	if v.verifyIat && !v.VerifyIssuedAt(claims, now, false) {
-		vErr.Inner = ErrTokenUsedBeforeIssued
-		vErr.Errors |= ValidationErrorIssuedAt
+	if v.verifyIat {
+		if err = v.verifyIssuedAt(claims, now, false); err != nil {
+			errs = append(errs, err)
+		}
 	}
 
 	// 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 v.expectedAud != "" {
+		if err = v.verifyAudience(claims, v.expectedAud, true); err != nil {
+			errs = append(errs, err)
+		}
 	}
 
 	// 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 v.expectedIss != "" {
+		if err = v.verifyIssuer(claims, v.expectedIss, true); err != nil {
+			errs = append(errs, err)
+		}
 	}
 
 	// 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
+	if v.expectedSub != "" {
+		if err = v.verifySubject(claims, v.expectedSub, true); err != nil {
+			errs = append(errs, err)
+		}
 	}
 
 	// Finally, we want to give the claim itself some possibility to do some
 	// additional custom validation based on a custom Validate function.
-	cvt, ok := claims.(interface {
-		Validate() error
-	})
+	cvt, ok := claims.(ClaimsValidator)
 	if ok {
 		if err := cvt.Validate(); err != nil {
-			vErr.Inner = err
-			vErr.Errors |= ValidationErrorClaimsInvalid
+			errs = append(errs, err)
 		}
 	}
 
-	if vErr.valid() {
+	if len(errs) == 0 {
 		return nil
 	}
 
-	return vErr
+	return joinErrors(errs...)
 }
 
-// VerifyExpiresAt compares the exp claim in claims against cmp. This function
-// will return true if cmp < exp. Additional leeway is taken into account.
+// verifyExpiresAt compares the exp claim in claims against cmp. This function
+// will succeed if cmp < exp. Additional leeway is taken into account.
 //
-// If exp is not set, it will return true if the claim is not required,
-// otherwise false will be returned.
+// If exp is not set, it will succeed if the claim is not required,
+// otherwise ErrTokenRequiredClaimMissing will be returned.
 //
 // Additionally, if any error occurs while retrieving the claim, e.g., when its
-// the wrong type, false will be returned.
-func (v *validator) VerifyExpiresAt(claims Claims, cmp time.Time, required bool) bool {
+// the wrong type, an ErrTokenUnverifiable error will be returned.
+func (v *validator) verifyExpiresAt(claims Claims, cmp time.Time, required bool) error {
 	exp, err := claims.GetExpirationTime()
 	if err != nil {
-		return false
+		return err
 	}
 
-	if exp != nil {
-		return cmp.Before((exp.Time).Add(+v.leeway))
-	} else {
-		return !required
+	if exp == nil {
+		return errorIfRequired(required, "exp")
 	}
+
+	return errorIfFalse(cmp.Before((exp.Time).Add(+v.leeway)), ErrTokenExpired)
 }
 
-// VerifyIssuedAt compares the iat claim in claims against cmp. This function
-// will return true if cmp >= iat. Additional leeway is taken into account.
+// verifyIssuedAt compares the iat claim in claims against cmp. This function
+// will succeed if cmp >= iat. Additional leeway is taken into account.
 //
-// If iat is not set, it will return true if the claim is not required,
-// otherwise false will be returned.
+// If iat is not set, it will succeed if the claim is not required,
+// otherwise ErrTokenRequiredClaimMissing will be returned.
 //
 // Additionally, if any error occurs while retrieving the claim, e.g., when its
-// the wrong type, false will be returned.
-func (v *validator) VerifyIssuedAt(claims Claims, cmp time.Time, required bool) bool {
+// the wrong type, an ErrTokenUnverifiable error will be returned.
+func (v *validator) verifyIssuedAt(claims Claims, cmp time.Time, required bool) error {
 	iat, err := claims.GetIssuedAt()
 	if err != nil {
-		return false
+		return err
 	}
 
-	if iat != nil {
-		return !cmp.Before(iat.Add(-v.leeway))
-	} else {
-		return !required
+	if iat == nil {
+		return errorIfRequired(required, "iat")
 	}
+
+	return errorIfFalse(!cmp.Before(iat.Add(-v.leeway)), ErrTokenUsedBeforeIssued)
 }
 
-// VerifyNotBefore compares the nbf claim in claims against cmp. This function
+// verifyNotBefore compares the nbf claim in claims against cmp. This function
 // will return true if cmp >= nbf. Additional leeway is taken into account.
 //
-// If nbf is not set, it will return true if the claim is not required,
-// otherwise false will be returned.
+// If nbf is not set, it will succeed if the claim is not required,
+// otherwise ErrTokenRequiredClaimMissing will be returned.
 //
 // Additionally, if any error occurs while retrieving the claim, e.g., when its
-// the wrong type, false will be returned.
-func (v *validator) VerifyNotBefore(claims Claims, cmp time.Time, required bool) bool {
+// the wrong type, an ErrTokenUnverifiable error will be returned.
+func (v *validator) verifyNotBefore(claims Claims, cmp time.Time, required bool) error {
 	nbf, err := claims.GetNotBefore()
 	if err != nil {
-		return false
+		return err
 	}
 
-	if nbf != nil {
-		return !cmp.Before(nbf.Add(-v.leeway))
-	} else {
-		return !required
+	if nbf == nil {
+		return errorIfRequired(required, "nbf")
 	}
+
+	return errorIfFalse(!cmp.Before(nbf.Add(-v.leeway)), ErrTokenNotValidYet)
 }
 
-// VerifyAudience compares the aud claim against cmp.
+// verifyAudience compares the aud claim against cmp.
 //
-// If aud is not set or an empty list, it will return true if the claim is not
-// required, otherwise false will be returned.
+// If aud is not set or an empty list, it will succeed if the claim is not required,
+// otherwise ErrTokenRequiredClaimMissing will be returned.
 //
 // Additionally, if any error occurs while retrieving the claim, e.g., when its
-// the wrong type, false will be returned.
-func (v *validator) VerifyAudience(claims Claims, cmp string, required bool) bool {
+// the wrong type, an ErrTokenUnverifiable error will be returned.
+func (v *validator) verifyAudience(claims Claims, cmp string, required bool) error {
 	aud, err := claims.GetAudience()
 	if err != nil {
-		return false
+		return err
 	}
 
 	if len(aud) == 0 {
-		return !required
+		return errorIfRequired(required, "aud")
 	}
 
 	// use a var here to keep constant time compare when looping over a number of claims
@@ -209,48 +234,68 @@ func (v *validator) VerifyAudience(claims Claims, cmp string, required bool) boo
 
 	// case where "" is sent in one or many aud claims
 	if stringClaims == "" {
-		return !required
+		return errorIfRequired(required, "aud")
 	}
 
-	return result
+	return errorIfFalse(result, ErrTokenInvalidAudience)
 }
 
-// VerifyIssuer compares the iss claim in claims against cmp.
+// verifyIssuer compares the iss claim in claims against cmp.
 //
-// If iss is not set, it will return true if the claim is not required,
-// otherwise false will be returned.
+// If iss is not set, it will succeed if the claim is not required,
+// otherwise ErrTokenRequiredClaimMissing will be returned.
 //
 // Additionally, if any error occurs while retrieving the claim, e.g., when its
-// the wrong type, false will be returned.
-func (v *validator) VerifyIssuer(claims Claims, cmp string, required bool) bool {
+// the wrong type, an ErrTokenUnverifiable error will be returned.
+func (v *validator) verifyIssuer(claims Claims, cmp string, required bool) error {
 	iss, err := claims.GetIssuer()
 	if err != nil {
-		return false
+		return err
 	}
 
 	if iss == "" {
-		return !required
+		return errorIfRequired(required, "iss")
 	}
 
-	return iss == cmp
+	return errorIfFalse(iss == cmp, ErrTokenInvalidIssuer)
 }
 
-// VerifySubject compares the sub claim against cmp.
+// verifySubject compares the sub claim against cmp.
 //
-// If sub is not set, it will return true if the claim is not required,
-// otherwise false will be returned.
+// If sub is not set, it will succeed if the claim is not required,
+// otherwise ErrTokenRequiredClaimMissing will be returned.
 //
 // Additionally, if any error occurs while retrieving the claim, e.g., when its
-// the wrong type, false will be returned.
-func (v *validator) VerifySubject(claims Claims, cmp string, required bool) bool {
+// the wrong type, an ErrTokenUnverifiable error will be returned.
+func (v *validator) verifySubject(claims Claims, cmp string, required bool) error {
 	sub, err := claims.GetSubject()
 	if err != nil {
-		return false
+		return err
 	}
 
 	if sub == "" {
-		return !required
+		return errorIfRequired(required, "sub")
 	}
 
-	return sub == cmp
+	return errorIfFalse(sub == cmp, ErrTokenInvalidSubject)
+}
+
+// errorIfFalse returns the error specified in err, if the value is true.
+// Otherwise, nil is returned.
+func errorIfFalse(value bool, err error) error {
+	if value {
+		return nil
+	} else {
+		return err
+	}
+}
+
+// errorIfRequired returns an ErrTokenRequiredClaimMissing error if required is
+// true. Otherwise, nil is returned.
+func errorIfRequired(required bool, claim string) error {
+	if required {
+		return newError(fmt.Sprintf("%s claim is required", claim), ErrTokenRequiredClaimMissing)
+	} else {
+		return nil
+	}
 }
diff --git a/validator_test.go b/validator_test.go
new file mode 100644
index 0000000..869b050
--- /dev/null
+++ b/validator_test.go
@@ -0,0 +1,261 @@
+package jwt
+
+import (
+	"errors"
+	"testing"
+	"time"
+)
+
+var ErrFooBar = errors.New("must be foobar")
+
+type MyCustomClaims struct {
+	Foo string `json:"foo"`
+	RegisteredClaims
+}
+
+func (m MyCustomClaims) Validate() error {
+	if m.Foo != "bar" {
+		return ErrFooBar
+	}
+	return nil
+}
+
+func Test_validator_Validate(t *testing.T) {
+	type fields struct {
+		leeway      time.Duration
+		timeFunc    func() time.Time
+		verifyIat   bool
+		expectedAud string
+		expectedIss string
+		expectedSub string
+	}
+	type args struct {
+		claims Claims
+	}
+	tests := []struct {
+		name    string
+		fields  fields
+		args    args
+		wantErr error
+	}{
+		{
+			name:    "expected iss mismatch",
+			fields:  fields{expectedIss: "me"},
+			args:    args{RegisteredClaims{Issuer: "not_me"}},
+			wantErr: ErrTokenInvalidIssuer,
+		},
+		{
+			name:    "expected iss is missing",
+			fields:  fields{expectedIss: "me"},
+			args:    args{RegisteredClaims{}},
+			wantErr: ErrTokenRequiredClaimMissing,
+		},
+		{
+			name:    "expected sub mismatch",
+			fields:  fields{expectedSub: "me"},
+			args:    args{RegisteredClaims{Subject: "not-me"}},
+			wantErr: ErrTokenInvalidSubject,
+		},
+		{
+			name:    "expected sub is missing",
+			fields:  fields{expectedSub: "me"},
+			args:    args{RegisteredClaims{}},
+			wantErr: ErrTokenRequiredClaimMissing,
+		},
+		{
+			name:    "custom validator",
+			fields:  fields{},
+			args:    args{MyCustomClaims{Foo: "not-bar"}},
+			wantErr: ErrFooBar,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			v := &validator{
+				leeway:      tt.fields.leeway,
+				timeFunc:    tt.fields.timeFunc,
+				verifyIat:   tt.fields.verifyIat,
+				expectedAud: tt.fields.expectedAud,
+				expectedIss: tt.fields.expectedIss,
+				expectedSub: tt.fields.expectedSub,
+			}
+			if err := v.Validate(tt.args.claims); (err != nil) && !errors.Is(err, tt.wantErr) {
+				t.Errorf("validator.Validate() error = %v, wantErr %v", err, tt.wantErr)
+			}
+		})
+	}
+}
+
+func Test_validator_verifyExpiresAt(t *testing.T) {
+	type fields struct {
+		leeway   time.Duration
+		timeFunc func() time.Time
+	}
+	type args struct {
+		claims   Claims
+		cmp      time.Time
+		required bool
+	}
+	tests := []struct {
+		name    string
+		fields  fields
+		args    args
+		wantErr error
+	}{
+		{
+			name:    "good claim",
+			fields:  fields{timeFunc: time.Now},
+			args:    args{claims: RegisteredClaims{ExpiresAt: NewNumericDate(time.Now().Add(10 * time.Minute))}},
+			wantErr: nil,
+		},
+		{
+			name:    "claims with invalid type",
+			fields:  fields{},
+			args:    args{claims: MapClaims{"exp": "string"}},
+			wantErr: ErrInvalidType,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			v := &validator{
+				leeway:   tt.fields.leeway,
+				timeFunc: tt.fields.timeFunc,
+			}
+
+			err := v.verifyExpiresAt(tt.args.claims, tt.args.cmp, tt.args.required)
+			if (err != nil) && !errors.Is(err, tt.wantErr) {
+				t.Errorf("validator.verifyExpiresAt() error = %v, wantErr %v", err, tt.wantErr)
+			}
+		})
+	}
+}
+
+func Test_validator_verifyIssuer(t *testing.T) {
+	type fields struct {
+		expectedIss string
+	}
+	type args struct {
+		claims   Claims
+		cmp      string
+		required bool
+	}
+	tests := []struct {
+		name    string
+		fields  fields
+		args    args
+		wantErr error
+	}{
+		{
+			name:    "good claim",
+			fields:  fields{expectedIss: "me"},
+			args:    args{claims: MapClaims{"iss": "me"}, cmp: "me"},
+			wantErr: nil,
+		},
+		{
+			name:    "claims with invalid type",
+			fields:  fields{expectedIss: "me"},
+			args:    args{claims: MapClaims{"iss": 1}, cmp: "me"},
+			wantErr: ErrInvalidType,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			v := &validator{
+				expectedIss: tt.fields.expectedIss,
+			}
+			err := v.verifyIssuer(tt.args.claims, tt.args.cmp, tt.args.required)
+			if (err != nil) && !errors.Is(err, tt.wantErr) {
+				t.Errorf("validator.verifyIssuer() error = %v, wantErr %v", err, tt.wantErr)
+			}
+		})
+	}
+}
+
+func Test_validator_verifySubject(t *testing.T) {
+	type fields struct {
+		expectedSub string
+	}
+	type args struct {
+		claims   Claims
+		cmp      string
+		required bool
+	}
+	tests := []struct {
+		name    string
+		fields  fields
+		args    args
+		wantErr error
+	}{
+		{
+			name:    "good claim",
+			fields:  fields{expectedSub: "me"},
+			args:    args{claims: MapClaims{"sub": "me"}, cmp: "me"},
+			wantErr: nil,
+		},
+		{
+			name:    "claims with invalid type",
+			fields:  fields{expectedSub: "me"},
+			args:    args{claims: MapClaims{"sub": 1}, cmp: "me"},
+			wantErr: ErrInvalidType,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			v := &validator{
+				expectedSub: tt.fields.expectedSub,
+			}
+			err := v.verifySubject(tt.args.claims, tt.args.cmp, tt.args.required)
+			if (err != nil) && !errors.Is(err, tt.wantErr) {
+				t.Errorf("validator.verifySubject() error = %v, wantErr %v", err, tt.wantErr)
+			}
+		})
+	}
+}
+
+func Test_validator_verifyIssuedAt(t *testing.T) {
+	type fields struct {
+		leeway    time.Duration
+		timeFunc  func() time.Time
+		verifyIat bool
+	}
+	type args struct {
+		claims   Claims
+		cmp      time.Time
+		required bool
+	}
+	tests := []struct {
+		name    string
+		fields  fields
+		args    args
+		wantErr error
+	}{
+		{
+			name:    "good claim without iat",
+			fields:  fields{verifyIat: true},
+			args:    args{claims: MapClaims{}, required: false},
+			wantErr: nil,
+		},
+		{
+			name:   "good claim with iat",
+			fields: fields{verifyIat: true},
+			args: args{
+				claims:   RegisteredClaims{IssuedAt: NewNumericDate(time.Now())},
+				cmp:      time.Now().Add(10 * time.Minute),
+				required: false,
+			},
+			wantErr: nil,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			v := &validator{
+				leeway:    tt.fields.leeway,
+				timeFunc:  tt.fields.timeFunc,
+				verifyIat: tt.fields.verifyIat,
+			}
+			if err := v.verifyIssuedAt(tt.args.claims, tt.args.cmp, tt.args.required); (err != nil) && !errors.Is(err, tt.wantErr) {
+				t.Errorf("validator.verifyIssuedAt() error = %v, wantErr %v", err, tt.wantErr)
+			}
+		})
+	}
+}