ResponseBuilder rbuilder = Response.fromResponse(response);
/* Common to simple and preflight */
rbuilder.header(CorsHeaderConstants.HEADER_AC_ALLOW_ORIGIN,
m.getExchange().get(CorsHeaderConstants.HEADER_ORIGIN));
rbuilder.header(CorsHeaderConstants.HEADER_AC_ALLOW_CREDENTIALS,
Boolean.toString(allowCredentials));
if (SIMPLE_REQUEST.equals(op)) {
/* 5.1.4 expose headers */
List<String> effectiveExposeHeaders