enable jwt.ParsePublicKeyFromPEM to parse PKCS1 Public Key (#120)

rsa_test.go

 package jwt_test
 
 import (
+	"bytes"
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/x509"
+	"encoding/pem"
 	"os"
 	"reflect"
 	"strings"
@@ -115,6 +120,17 @@ func TestRSAKeyParsing(t *testing.T) {
 	pubKey, _ := os.ReadFile("test/sample_key.pub")
 	badKey := []byte("All your base are belong to key")
 
+	randomKey, err := rsa.GenerateKey(rand.Reader, 2048)
+	if err != nil {
+		t.Errorf("Failed to generate RSA private key: %v", err)
+	}
+
+	publicKeyBytes := x509.MarshalPKCS1PublicKey(&randomKey.PublicKey)
+	pkcs1Buffer := new(bytes.Buffer)
+	if err = pem.Encode(pkcs1Buffer, &pem.Block{Type: "RSA PUBLIC KEY", Bytes: publicKeyBytes}); err != nil {
+		t.Errorf("Failed to encode public pem: %v", err)
+	}
+
 	// Test parsePrivateKey
 	if _, e := jwt.ParseRSAPrivateKeyFromPEM(key); e != nil {
 		t.Errorf("Failed to parse valid private key: %v", e)
@@ -149,6 +165,9 @@ func TestRSAKeyParsing(t *testing.T) {
 		t.Errorf("Parsed invalid key as valid private key: %v", k)
 	}
 
+	if _, err := jwt.ParseRSAPublicKeyFromPEM(pkcs1Buffer.Bytes()); err != nil {
+		t.Errorf("failed to parse RSA public key: %v", err)
+	}
 }
 
 func BenchmarkRSAParsing(b *testing.B) {

rsa_utils.go

@@ -75,7 +75,7 @@ func ParseRSAPrivateKeyFromPEMWithPassword(key []byte, password string) (*rsa.Pr
 	return pkey, nil
 }
 
-// ParseRSAPublicKeyFromPEM parses a PEM encoded PKCS1 or PKCS8 public key
+// ParseRSAPublicKeyFromPEM parses a certificate or a PEM encoded PKCS1 or PKIX public key
 func ParseRSAPublicKeyFromPEM(key []byte) (*rsa.PublicKey, error) {
 	var err error
 
@@ -91,7 +91,9 @@ func ParseRSAPublicKeyFromPEM(key []byte) (*rsa.PublicKey, error) {
 		if cert, err := x509.ParseCertificate(block.Bytes); err == nil {
 			parsedKey = cert.PublicKey
 		} else {
-			return nil, err
+			if parsedKey, err = x509.ParsePKCS1PublicKey(block.Bytes); err != nil {
+				return nil, err
+			}
 		}
 	}