feat(crypto): hash algorithm for EdDSA (#638)

* feat(crypto): hash algorithm for EdDSA

* update code comment

* rp: modify keytype check to support EdDSA

* example: signing algs from discovery

---------

Co-authored-by: Livio Spring <livio.a@gmail.com>

pkg/crypto/hash.go

@@ -21,6 +21,14 @@ func GetHashAlgorithm(sigAlgorithm jose.SignatureAlgorithm) (hash.Hash, error) {
 		return sha512.New384(), nil
 	case jose.RS512, jose.ES512, jose.PS512:
 		return sha512.New(), nil
+
+	// There is no published spec for this yet, but we have confirmation it will get published.
+	// There is consensus here: https://bitbucket.org/openid/connect/issues/1125/_hash-algorithm-for-eddsa-id-tokens
+	// Currently Go and go-jose only supports the ed25519 curve key for EdDSA, so we can safely assume sha512 here.
+	// It is unlikely ed448 will ever be supported: https://github.com/golang/go/issues/29390
+	case jose.EdDSA:
+		return sha512.New(), nil
+
 	default:
 		return nil, fmt.Errorf("%w: %q", ErrUnsupportedAlgorithm, sigAlgorithm)
 	}

pkg/oidc/keyset.go

@@ -6,6 +6,7 @@ import (
 	"crypto/ed25519"
 	"crypto/rsa"
 	"errors"
+	"strings"
 
 	jose "github.com/go-jose/go-jose/v4"
 )
@@ -92,17 +93,17 @@ func FindMatchingKey(keyID, use, expectedAlg string, keys ...jose.JSONWebKey) (k
 }
 
 func algToKeyType(key any, alg string) bool {
-	switch alg[0] {
-	case 'R', 'P':
+	if strings.HasPrefix(alg, "RS") || strings.HasPrefix(alg, "PS") {
 		_, ok := key.(*rsa.PublicKey)
 		return ok
-	case 'E':
+	}
+	if strings.HasPrefix(alg, "ES") {
 		_, ok := key.(*ecdsa.PublicKey)
 		return ok
-	case 'O':
-		_, ok := key.(*ed25519.PublicKey)
-		return ok
-	default:
-		return false
 	}
+	if alg == string(jose.EdDSA) {
+		_, ok := key.(ed25519.PublicKey)
+		return ok
+	}
+	return false
 }