public ClientFactoryBuilder proxyConfig(ProxyConfigSelector proxyConfigSelector) {
        requireNonNull(proxyConfigSelector, "proxyConfigSelector");
        option(ClientFactoryOptions.PROXY_CONFIG_SELECTOR, proxyConfigSelector);
        return this;
    }
Sets the {@link ProxyConfigSelector} which determines the {@link ProxyConfig} to be used.
core/src/main/java/com/linecorp/armeria/client/ClientFactoryBuilder.java