/**
 * Global option to specify a header to be added to every request,
 * if the request does not already contain such a header.
 */
Builder defaultHeader(String header, String... values);

/**
 * Provide a consumer to customize every request being built.
 * @param defaultRequest the consumer to use for modifying requests
 */
Builder defaultRequest(Consumer<RequestHeadersSpec<?>> defaultRequest);

// DefaultWebClientTests.java
@Test
void defaultRequest_override() {
	ThreadLocal<String> context = new NamedThreadLocal<>("foo");

	WebClient client = this.builder
			.defaultRequest(spec -> spec.accept(MediaType.APPLICATION_JSON)) // default
			.build();

	client.get().uri("/path")
			.accept(MediaType.IMAGE_PNG) // set
			.retrieve().bodyToMono(Void.class).block(Duration.ofSeconds(10));

	ClientRequest request = verifyAndGetRequest();
	assertThat(request.headers().getAccept()).isEqualTo(MediaType.IMAGE_PNG); // ❌Expected: <image/png> but actual: <application/json>
}