Allow to choose if extractable or not

src/secret-wrap.ts

@@ -12,14 +12,14 @@ export class SecretWrap {
         private readonly iv: Uint8Array,
     ) {}
 
-    public static gen_key() : Promise<CryptoKey> {
+    public static gen_key(extractable : boolean = true) : Promise<CryptoKey> {
         log.trace("generate key")
         return crypto.subtle.generateKey(
             {
                 name: "AES-GCM",
                 length: 256,
             },
-            true,
+            extractable,
             ["wrapKey", "unwrapKey"],
         )
     }