1 files changed, 83 insertions, 0 deletions
diff --git a/backend/auth/dpop.go b/backend/auth/dpop.go
new file mode 100644
index 0000000..2a8f6ed
--- /dev/null
+++ b/backend/auth/dpop.go
@@ -0,0 +1,83 @@
+package auth
+
+import (
+	"crypto"
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"crypto/rand"
+	"encoding/base64"
+	"time"
+
+	"github.com/golang-jwt/jwt/v5"
+)
+
+type DPoPKeyPair struct {
+	PrivateKey *ecdsa.PrivateKey
+	PublicKey  *ecdsa.PublicKey
+	JWK        map[string]string
+}
+
+func GenerateDPoPKeyPair() (*DPoPKeyPair, error) {
+	privateKey, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
+	if err != nil {
+		return nil, err
+	}
+
+	jwk := map[string]string{
+		"kty": "EC",
+		"crv": "P-256",
+		"x":   base64.RawURLEncoding.EncodeToString(privateKey.PublicKey.X.Bytes()),
+		"y":   base64.RawURLEncoding.EncodeToString(privateKey.PublicKey.Y.Bytes()),
+	}
+
+	return &DPoPKeyPair{
+		PrivateKey: privateKey,
+		PublicKey:  &privateKey.PublicKey,
+		JWK:        jwk,
+	}, nil
+}
+
+func (kp *DPoPKeyPair) GenerateDPoPProof(method, url, nonce string) (string, error) {
+	// generate unique ID for this proof
+	jti, err := GenerateRandomToken()
+	if err != nil {
+		return "", err
+	}
+
+	// create JWT header with JWK
+	header := map[string]interface{}{
+		"typ": "dpop+jwt",
+		"alg": "ES256",
+		"jwk": kp.JWK,
+	}
+
+	// create JWT claims
+	claims := jwt.MapClaims{
+		"jti": jti,
+		"htm": method,  // HTTP method (GET, POST, etc)
+		"htu": url,     // HTTP URL (the endpoint you're calling)
+		"iat": time.Now().Unix(),
+	}
+
+	// add nonce if provided
+	if nonce != "" {
+		claims["nonce"] = nonce
+	}
+
+	// create token with custom header
+	token := jwt.NewWithClaims(&jwt.SigningMethodECDSA{
+		Name:      "ES256",
+		Hash:      crypto.SHA256,
+		KeySize:   32,
+		CurveBits: 256,
+	}, claims)
+	token.Header = header
+
+	// sign with private key
+	tokenString, err := token.SignedString(kp.PrivateKey)
+	if err != nil {
+		return "", err
+	}
+
+	return tokenString, nil
+}