How to post request with spring boot web-client for Form data for content type application/x-www-form-urlencoded

We can use BodyInserters.fromFormData for this purpose

webClient client = WebClient.builder()
        .baseUrl("SOME-BASE-URL")
        .defaultHeader(HttpHeaders.CONTENT_TYPE, MediaType.APPLICATION_FORM_URLENCODED_VALUE)
        .build();

return client.post()
        .uri("SOME-URI)
        .body(BodyInserters.fromFormData("username", "SOME-USERNAME")
                .with("password", "SONE-PASSWORD"))
                .retrieve()
                .bodyToFlux(SomeClass.class)
                .onErrorMap(e -> new MyException("messahe",e))
        .blockLast();
    

In another form:

MultiValueMap<String, String> formData = new LinkedMultiValueMap<>();
formData.add("username", "XXXX");
formData.add("password", "XXXX");

String response = WebClient.create()
    .post()
    .uri("URL")
    .contentType(MediaType.APPLICATION_FORM_URLENCODED)
    .body(BodyInserters.fromFormData(formData))
    .exchange()
    .block()
    .bodyToMono(String.class)
    .block();

In my humble opinion, for simple request, REST Assured is easier to use.