default FilterType filterType() {
        Filter f = getClass().getAnnotation(Filter.class);
        if (f != null) {
            return f.type();
        }
        throw new UnsupportedOperationException("not implemented");
    }
to classify a filter by type. Standard types in Zuul are "in" for pre-routing filtering,
"end" for routing to an origin, "out" for post-routing filters.

@return FilterType
zuul-core/src/main/java/com/netflix/zuul/filters/ZuulFilter.java