@Test
    void testAllowAllHeaders() {
        final WebClient client = client();

        HttpRequest preflightReq = HttpRequest.of(
                RequestHeaders.of(HttpMethod.OPTIONS, "/cors13",
                                  HttpHeaderNames.ORIGIN, "http://example.com",
                                  HttpHeaderNames.ACCESS_CONTROL_REQUEST_METHOD, "GET",
                                  HttpHeaderNames.ACCESS_CONTROL_REQUEST_HEADERS, "foo,bar"));
        AggregatedHttpResponse res = client.execute(preflightReq).aggregate().join();
        assertThat(res.status()).isEqualTo(HttpStatus.OK);
        assertThat(res.headers().get(HttpHeaderNames.ACCESS_CONTROL_ALLOW_ORIGIN))
                .isEqualTo("http://example.com");
        assertThat(res.headers().get(HttpHeaderNames.ACCESS_CONTROL_ALLOW_METHODS)).isEqualTo("GET");
        assertThat(res.headers().get(HttpHeaderNames.ACCESS_CONTROL_ALLOW_HEADERS)).isEqualTo("foo,bar");

        preflightReq = HttpRequest.of(
                RequestHeaders.of(HttpMethod.OPTIONS, "/cors13",
                                  HttpHeaderNames.ORIGIN, "http://example.com",
                                  HttpHeaderNames.ACCESS_CONTROL_REQUEST_METHOD, "GET"));
        res = client.execute(preflightReq).aggregate().join();
        assertThat(res.status()).isEqualTo(HttpStatus.OK);
        assertThat(res.headers().get(HttpHeaderNames.ACCESS_CONTROL_ALLOW_ORIGIN))
                .isEqualTo("http://example.com");
        assertThat(res.headers().get(HttpHeaderNames.ACCESS_CONTROL_ALLOW_METHODS)).isEqualTo("GET");
        assertThat(res.headers().get(HttpHeaderNames.ACCESS_CONTROL_ALLOW_HEADERS)).isNull();
    }
If no CORS was configured and there's no binding for OPTIONS method, the server's fallback service will
be matched and the service with partial binding must not be invoked.
core/src/test/java/com/linecorp/armeria/server/cors/HttpServerCorsTest.java