如果你借用this solution中关于给现有prometheus执行器指标添加自定义标记的方法，并解析你感兴趣的属性的请求（我使用Jackson对象Map器），它应该能完成这个任务，看起来像下面这样：

@Bean
public WebMvcTagsContributor webMvcTagsContributor() {

    return new WebMvcTagsContributor() {
        @Override
        public Iterable<Tag> getTags(
            HttpServletRequest request,
            HttpServletResponse response,
            Object handler,
            Throwable exception
        ) {

            // parse the request body to get the property we're interested in later
            ObjectMapper mapper = new ObjectMapper();
            ThingToMapFromRequestBody bodyAsObject = null;
            try {
                bodyAsObject = mapper.readValue(request.getReader().lines().collect(Collectors.joining()),
                    ThingToMapFromRequestBody.class
                );
            } catch (IOException e) {
                e.printStackTrace();
            }

            // add the property we're interested in to our metrics
            Tags tags = Tags.empty();
            tags = tags.and(Tag.of("challenge", bodyAsObject != null ? bodyAsObject.type() : ""));
            return tags;
        }

        @Override
        public Iterable<Tag> getLongRequestTags(HttpServletRequest request, Object handler) {

            return null;
        }
    };
}

// making use of a record rather than class, introduced in Java 14
record ThingToMapFromRequestBody(String type, String method) { }