.

vendor/github.com/MicahParks/keyfunc/v2/rsa.go

@@ -0,0 +1,43 @@
+package keyfunc
+
+import (
+	"crypto/rsa"
+	"fmt"
+	"math/big"
+)
+
+const (
+	// ktyRSA is the key type (kty) in the JWT header for RSA.
+	ktyRSA = "RSA"
+)
+
+// RSA parses a jsonWebKey and turns it into an RSA public key.
+func (j *jsonWebKey) RSA() (publicKey *rsa.PublicKey, err error) {
+	if j.Exponent == "" || j.Modulus == "" {
+		return nil, fmt.Errorf("%w: %s", ErrMissingAssets, ktyRSA)
+	}
+
+	// Decode the exponent from Base64.
+	//
+	// According to RFC 7518, this is a Base64 URL unsigned integer.
+	// https://tools.ietf.org/html/rfc7518#section-6.3
+	exponent, err := base64urlTrailingPadding(j.Exponent)
+	if err != nil {
+		return nil, err
+	}
+	modulus, err := base64urlTrailingPadding(j.Modulus)
+	if err != nil {
+		return nil, err
+	}
+
+	publicKey = &rsa.PublicKey{}
+
+	// Turn the exponent into an integer.
+	//
+	// According to RFC 7517, these numbers are in big-endian format.
+	// https://tools.ietf.org/html/rfc7517#appendix-A.1
+	publicKey.E = int(big.NewInt(0).SetBytes(exponent).Uint64())
+	publicKey.N = big.NewInt(0).SetBytes(modulus)
+
+	return publicKey, nil
+}