.

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

@@ -0,0 +1,69 @@
+package keyfunc
+
+import (
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"errors"
+	"fmt"
+	"math/big"
+)
+
+const (
+	// ktyEC is the key type (kty) in the JWT header for ECDSA.
+	ktyEC = "EC"
+
+	// p256 represents a 256-bit cryptographic elliptical curve type.
+	p256 = "P-256"
+
+	// p384 represents a 384-bit cryptographic elliptical curve type.
+	p384 = "P-384"
+
+	// p521 represents a 521-bit cryptographic elliptical curve type.
+	p521 = "P-521"
+)
+
+var (
+	// ErrECDSACurve indicates an error with the ECDSA curve.
+	ErrECDSACurve = errors.New("invalid ECDSA curve")
+)
+
+// ECDSA parses a jsonWebKey and turns it into an ECDSA public key.
+func (j *jsonWebKey) ECDSA() (publicKey *ecdsa.PublicKey, err error) {
+	if j.X == "" || j.Y == "" || j.Curve == "" {
+		return nil, fmt.Errorf("%w: %s", ErrMissingAssets, ktyEC)
+	}
+
+	// Decode the X coordinate from Base64.
+	//
+	// According to RFC 7518, this is a Base64 URL unsigned integer.
+	// https://tools.ietf.org/html/rfc7518#section-6.3
+	xCoordinate, err := base64urlTrailingPadding(j.X)
+	if err != nil {
+		return nil, err
+	}
+	yCoordinate, err := base64urlTrailingPadding(j.Y)
+	if err != nil {
+		return nil, err
+	}
+
+	publicKey = &ecdsa.PublicKey{}
+	switch j.Curve {
+	case p256:
+		publicKey.Curve = elliptic.P256()
+	case p384:
+		publicKey.Curve = elliptic.P384()
+	case p521:
+		publicKey.Curve = elliptic.P521()
+	default:
+		return nil, fmt.Errorf("%w: unknown curve: %s", ErrECDSACurve, j.Curve)
+	}
+
+	// Turn the X coordinate into *big.Int.
+	//
+	// According to RFC 7517, these numbers are in big-endian format.
+	// https://tools.ietf.org/html/rfc7517#appendix-A.1
+	publicKey.X = big.NewInt(0).SetBytes(xCoordinate)
+	publicKey.Y = big.NewInt(0).SetBytes(yCoordinate)
+
+	return publicKey, nil
+}