chore: 🤖 tweak oidc attributes serialization

addons/api/addon/models/fragment-auth-method-attributes.js

@@ -9,10 +9,10 @@ export default class FragmentAuthMethodAttributesModel extends Fragment {
   @attr('string') issuer;
   @attr('string') client_id;
   @attr('string') client_secret;
-  @attr('string') client_secret_hmac;
+  @attr('string', { readOnly: true }) client_secret_hmac;
   @attr('number') max_age;
   @attr('string') api_url_prefix;
-  @attr('string') callback_url;
+  @attr('string', { readOnly: true }) callback_url;
   @attr('boolean') disable_discovered_config_validation;
   @attr('boolean') dry_run;