Adding canonical Keyfunc functions for RSA, ECDSA, EdDSA and HMAC

This PR adds ready-to-use keyfunc functions for the various signing methods. This should simplify a lot of standard use-cases and also includes a proper signing method check.

ecdsa.go

@@ -140,3 +140,10 @@ func (m *SigningMethodECDSA) Sign(signingString string, key interface{}) (string
 		return "", err
 	}
 }
+
+// ECDSAPublicKey represents a [Keyfunc] that returns the ECDSA key specified in
+// key. Furthermore, it checks, whether the signing method matches
+// [SigningMethodECDSA].
+func ECDSAPublicKey(key *ecdsa.PublicKey) Keyfunc {
+	return secureKeyFunc(key, []string{"ES256", "ES384", "ES512"})
+}

ed25519.go

@@ -83,3 +83,10 @@ func (m *SigningMethodEd25519) Sign(signingString string, key interface{}) (stri
 	}
 	return EncodeSegment(sig), nil
 }
+
+// Ed25519PublicKey represents a [Keyfunc] that returns the Ed25519 key
+// specified in key. Furthermore, it checks, whether the signing method matches
+// [SigningMethodEdDSA].
+func Ed25519PublicKey(key ed25519.PublicKey) Keyfunc {
+	return secureKeyFunc(key, []string{"EdDSA"})
+}

example_test.go

@@ -80,9 +80,7 @@ func ExampleParseWithClaims_customClaimsType() {
 		jwt.RegisteredClaims
 	}
 
-	token, err := jwt.ParseWithClaims(tokenString, &MyCustomClaims{}, func(token *jwt.Token) (interface{}, error) {
-		return []byte("AllYourBase"), nil
-	})
+	token, err := jwt.ParseWithClaims(tokenString, &MyCustomClaims{}, jwt.PresharedKey([]byte("AllYourBase")))
 
 	if claims, ok := token.Claims.(*MyCustomClaims); ok && token.Valid {
 		fmt.Printf("%v %v", claims.Foo, claims.RegisteredClaims.Issuer)
@@ -103,9 +101,11 @@ func ExampleParseWithClaims_validationOptions() {
 		jwt.RegisteredClaims
 	}
 
-	token, err := jwt.ParseWithClaims(tokenString, &MyCustomClaims{}, func(token *jwt.Token) (interface{}, error) {
-		return []byte("AllYourBase"), nil
-	}, jwt.WithLeeway(5*time.Second))
+	token, err := jwt.ParseWithClaims(
+		tokenString, &MyCustomClaims{},
+		jwt.PresharedKey([]byte("AllYourBase")),
+		jwt.WithLeeway(5*time.Second),
+	)
 
 	if claims, ok := token.Claims.(*MyCustomClaims); ok && token.Valid {
 		fmt.Printf("%v %v", claims.Foo, claims.RegisteredClaims.Issuer)
@@ -138,9 +138,10 @@ func (m MyCustomClaims) Validate() error {
 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))
+	token, err := jwt.ParseWithClaims(
+		tokenString, &MyCustomClaims{},
+		jwt.PresharedKey([]byte("AllYourBase")),
+		jwt.WithLeeway(5*time.Second))
 
 	if claims, ok := token.Claims.(*MyCustomClaims); ok && token.Valid {
 		fmt.Printf("%v %v", claims.Foo, claims.RegisteredClaims.Issuer)
@@ -156,9 +157,7 @@ func ExampleParse_errorChecking() {
 	// Token from another example.  This token is expired
 	var tokenString = "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJmb28iOiJiYXIiLCJleHAiOjE1MDAwLCJpc3MiOiJ0ZXN0In0.HE7fK0xOQwFEr4WDgRWj4teRPZ6i3GLwD5YCm6Pwu_c"
 
-	token, err := jwt.Parse(tokenString, func(token *jwt.Token) (interface{}, error) {
-		return []byte("AllYourBase"), nil
-	})
+	token, err := jwt.Parse(tokenString, jwt.PresharedKey([]byte("AllYourBase")))
 
 	if token.Valid {
 		fmt.Println("You look nice today")

hmac.go

@@ -93,3 +93,8 @@ func (m *SigningMethodHMAC) Sign(signingString string, key interface{}) (string,
 
 	return "", ErrInvalidKeyType
 }
+
+// PresharedKey represents a [Keyfunc] that simply returns the key specified in the byte slice.
+func PresharedKey(key []byte) Keyfunc {
+	return secureKeyFunc(key, []string{"HS256", "HS384", "HS512"})
+}

parser.go

@@ -3,7 +3,6 @@ package jwt
 import (
 	"bytes"
 	"encoding/json"
-	"fmt"
 	"strings"
 )
 
@@ -55,17 +54,8 @@ func (p *Parser) ParseWithClaims(tokenString string, claims Claims, keyFunc Keyf
 
 	// Verify signing method is in the required set
 	if p.validMethods != nil {
-		var signingMethodValid = false
-		var alg = token.Method.Alg()
-		for _, m := range p.validMethods {
-			if m == alg {
-				signingMethodValid = true
-				break
-			}
-		}
-		if !signingMethodValid {
-			// signing method is not in the listed set
-			return token, newError(fmt.Sprintf("signing method %v is invalid", alg), ErrTokenSignatureInvalid)
+		if err = token.hasValidSigningMethod(p.validMethods); err != nil {
+			return token, err
 		}
 	}
 

rsa.go

@@ -99,3 +99,10 @@ func (m *SigningMethodRSA) Sign(signingString string, key interface{}) (string,
 		return "", err
 	}
 }
+
+// RSAPublicKey represents a [Keyfunc] that returns the RSA key specified in
+// key. Furthermore, it checks, whether the signing method matches
+// [SigningMethodRSA].
+func RSAPublicKey(key *rsa.PublicKey) Keyfunc {
+	return secureKeyFunc(key, []string{"RS256", "RS384", "RS512"})
+}

test/helpers.go

@@ -2,6 +2,7 @@ package test
 
 import (
 	"crypto"
+	"crypto/ecdsa"
 	"crypto/rsa"
 	"os"
 
@@ -56,7 +57,7 @@ func LoadECPrivateKeyFromDisk(location string) crypto.PrivateKey {
 	return key
 }
 
-func LoadECPublicKeyFromDisk(location string) crypto.PublicKey {
+func LoadECPublicKeyFromDisk(location string) *ecdsa.PublicKey {
 	keyData, e := os.ReadFile(location)
 	if e != nil {
 		panic(e.Error())

token.go

@@ -3,6 +3,7 @@ package jwt
 import (
 	"encoding/base64"
 	"encoding/json"
+	"fmt"
 	"strings"
 )
 
@@ -143,3 +144,36 @@ func DecodeSegment(seg string) ([]byte, error) {
 	}
 	return encoding.DecodeString(seg)
 }
+
+// secureKeyFunc returns a secure [Keyfunc] for the specified key that also
+// includes a signing method check.
+func secureKeyFunc(key any, validMethods []string) Keyfunc {
+	return func(t *Token) (interface{}, error) {
+		// Check, if the signing method matches
+		if err := t.hasValidSigningMethod(validMethods); err != nil {
+			return nil, err
+		}
+
+		return key, nil
+	}
+}
+
+// hasValidSigningMethod is a utility function that checks, if the signing
+// method of the token is included in the validMethods slice.
+func (token *Token) hasValidSigningMethod(validMethods []string) error {
+	var signingMethodValid = false
+	var alg = token.Method.Alg()
+	for _, m := range validMethods {
+		if m == alg {
+			signingMethodValid = true
+			break
+		}
+	}
+
+	if !signingMethodValid {
+		// signing method is not in the listed set
+		return newError(fmt.Sprintf("signing method %v is invalid", alg), ErrTokenSignatureInvalid)
+	}
+
+	return nil
+}

token_test.go

@@ -1,17 +1,17 @@
-package jwt_test
+package jwt
 
 import (
+	"errors"
+	"reflect"
 	"testing"
-
-	"github.com/golang-jwt/jwt/v5"
 )
 
 func TestToken_SigningString(t1 *testing.T) {
 	type fields struct {
 		Raw       string
-		Method    jwt.SigningMethod
+		Method    SigningMethod
 		Header    map[string]interface{}
-		Claims    jwt.Claims
+		Claims    Claims
 		Signature string
 		Valid     bool
 	}
@@ -25,12 +25,12 @@ func TestToken_SigningString(t1 *testing.T) {
 			name: "",
 			fields: fields{
 				Raw:    "",
-				Method: jwt.SigningMethodHS256,
+				Method: SigningMethodHS256,
 				Header: map[string]interface{}{
 					"typ": "JWT",
-					"alg": jwt.SigningMethodHS256.Alg(),
+					"alg": SigningMethodHS256.Alg(),
 				},
-				Claims:    jwt.RegisteredClaims{},
+				Claims:    RegisteredClaims{},
 				Signature: "",
 				Valid:     false,
 			},
@@ -40,7 +40,7 @@ func TestToken_SigningString(t1 *testing.T) {
 	}
 	for _, tt := range tests {
 		t1.Run(tt.name, func(t1 *testing.T) {
-			t := &jwt.Token{
+			t := &Token{
 				Raw:       tt.fields.Raw,
 				Method:    tt.fields.Method,
 				Header:    tt.fields.Header,
@@ -61,13 +61,13 @@ func TestToken_SigningString(t1 *testing.T) {
 }
 
 func BenchmarkToken_SigningString(b *testing.B) {
-	t := &jwt.Token{
-		Method: jwt.SigningMethodHS256,
+	t := &Token{
+		Method: SigningMethodHS256,
 		Header: map[string]interface{}{
 			"typ": "JWT",
-			"alg": jwt.SigningMethodHS256.Alg(),
+			"alg": SigningMethodHS256.Alg(),
 		},
-		Claims: jwt.RegisteredClaims{},
+		Claims: RegisteredClaims{},
 	}
 	b.Run("BenchmarkToken_SigningString", func(b *testing.B) {
 		b.ResetTimer()
@@ -77,3 +77,48 @@ func BenchmarkToken_SigningString(b *testing.B) {
 		}
 	})
 }
+
+func Test_secureKeyFunc(t *testing.T) {
+	type fields struct {
+		token *Token
+	}
+	type args struct {
+		key          any
+		validMethods []string
+	}
+	tests := []struct {
+		name    string
+		fields  fields
+		args    args
+		wantKey any
+		wantErr error
+	}{
+		{
+			name:    "invalid method",
+			fields:  fields{&Token{Header: map[string]interface{}{"alg": "RS512"}, Method: SigningMethodRS512}},
+			args:    args{key: []byte("mysecret"), validMethods: []string{"HS256"}},
+			wantKey: nil,
+			wantErr: ErrTokenSignatureInvalid,
+		},
+		{
+			name:    "correct method",
+			fields:  fields{&Token{Header: map[string]interface{}{"alg": "HS256"}, Method: SigningMethodHS256}},
+			args:    args{key: []byte("mysecret"), validMethods: []string{"HS256"}},
+			wantKey: []byte("mysecret"),
+			wantErr: nil,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			keyfunc := secureKeyFunc(tt.args.key, tt.args.validMethods)
+			gotKey, gotErr := keyfunc(tt.fields.token)
+
+			if !reflect.DeepEqual(gotKey, tt.wantKey) {
+				t.Errorf("secureKeyFunc() key = %v, want %v", gotKey, tt.wantKey)
+			}
+			if (gotErr != nil) && !errors.Is(gotErr, tt.wantErr) {
+				t.Errorf("secureKeyFunc() err = %v, want %v", gotErr, tt.wantErr)
+			}
+		})
+	}
+}