public Optional<Integer> getProxyPort() {
        return Optional.ofNullable(proxyPort);
    }
Returns either the proxyPort set on this object, or
if not provided, checks the value of the Java system property
for proxy port according to {@link #getProtocol()}: i.e. if
protocol is https, returns the value of the system property
https.proxyPort, otherwise returns value of http.proxyPort.

@return The proxy port the client will connect through.
aws-java-sdk-opensdk/src/main/java/com/amazonaws/opensdk/config/ProxyConfiguration.java