public Optional<String> getProxyHost() {
        return Optional.ofNullable(proxyHost);
    }
Returns the optional proxy host the client will connect through.
Returns either the proxyHost set on this object, or if not provided,
checks the value of the Java system property for proxy host according to {@link #getProtocol()}:
i.e. if protocol is https, returns the value of the system property https.proxyHost,
otherwise returns value of http.proxyHost.

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