code: @PostMapping(
        value = "/{entityTypeId}/{id}",
        params = "_method=GET",
        produces = APPLICATION_JSON_VALUE)
    @ResponseBody
    public Map<String, Object> retrieveEntity(
        @PathVariable("entityTypeId") String entityTypeId,
        @PathVariable("id") String untypedId,
        @Valid @RequestBody EntityTypeRequest request) {
      Set<String> attributesSet = toAttributeSet(request != null ? request.getAttributes() : null);
      Map<String, Set<String>> attributeExpandSet =
          toExpandMap(request != null ? request.getExpand() : null);
  
      EntityType meta = dataService.getEntityType(entityTypeId);
      Object id = getTypedValue(untypedId, meta.getIdAttribute());
      Entity entity = dataService.findOneById(entityTypeId, id);
  
      if (entity == null) {
        throw new UnknownEntityException(meta, untypedId);
      }
  
      return getEntityAsMap(entity, meta, attributesSet, attributeExpandSet);
    }
docs: Same as retrieveEntity (GET) only tunneled through POST.