private String wrapperHeaders(final String headers) {
            final Set<String> headerSet = DEFAULT_ALLOWED_HEADERS;
            if (StringUtils.isNotEmpty(headers)) {
                headerSet.addAll(Stream.of(headers.split(",")).collect(Collectors.toSet()));
            }
            return String.join(",", headerSet);
        }
wrapper the headers.

@param headers headers
@return wrapped headers
shenyu-common/src/main/java/org/apache/shenyu/common/config/ShenyuConfig.java