public Set<String> allowedRequestHeaders() {
        return Collections.unmodifiableSet(allowedRequestHeaders);
    }
@Test
    public void requestHeaders() {
        final CorsConfig cors = forAnyOrigin().allowedRequestHeaders("preflight-header1", "preflight-header2").build();
        assertThat(cors.allowedRequestHeaders(), hasItems("preflight-header1", "preflight-header2"));
    }