public Optional<Boolean> isPreemptiveBasicProxyAuth() {
        return Optional.ofNullable(preemptiveBasicProxyAuth);
    }
Returns whether to attempt to authenticate preemptively against proxy servers using basic
authentication.

@return Whether to authenticate preemptively against proxy server.
aws-java-sdk-opensdk/src/main/java/com/amazonaws/opensdk/config/ProxyConfiguration.java