Fix EdDSA algorithm

src/Library/Signature/Algorithm/EdDSA.php

@@ -40,7 +40,7 @@ public function sign(JWK $key, string $input): string
             throw new InvalidArgumentException('Invalid "d" parameter.');
         }
         if (! $key->has('x')) {
-            $x = sodium_crypto_sign_publickey_from_secretkey($d);
+            $x = $this->getPublicKey($key);
         } else {
             $x = $key->get('x');
         }
@@ -84,6 +84,21 @@ public function name(): string
         return 'EdDSA';
     }
 
+    private static function getPublicKey(JWK $key): string
+    {
+        switch ($key->get('crv')) {
+            case 'Ed25519':
+                return Ed25519::publickey_from_secretkey($key->get('d'));
+            case 'X25519':
+                if (extension_loaded('sodium')) {
+                    return sodium_crypto_scalarmult_base($key->get('d'));
+                }
+                // no break
+            default:
+                throw new InvalidArgumentException('Unsupported key type');
+        }
+    }
+
     private function checkKey(JWK $key): void
     {
         if (! in_array($key->get('kty'), $this->allowedKeyTypes(), true)) {