@Override
    protected void doApply(ApiResponse response, IPolicyContext context, UniqueHeaderBean config,
                           IPolicyChain<ApiResponse> chain) {

        if (TRUE.equals(config.getResponseHeader())) {
            final String uniqueValue = context.getAttribute(UNIQUE_HEADER_KEY, null);
            if (nonNull(uniqueValue)) {
                response.getHeaders().put(config.getHeaderName(), uniqueValue);
            }
        }
        super.doApply(response, context, config, chain);
    }
@see io.apiman.gateway.engine.policies.AbstractMappedPolicy#doApply(io.apiman.gateway.engine.beans.ApiRequest, io.apiman.gateway.engine.policy.IPolicyContext, java.lang.Object, io.apiman.gateway.engine.policy.IPolicyChain)
plugins/unique-header-policy/src/main/java/io/apiman/plugins/uniqueheader/UniqueHeaderPolicy.java