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

@return The password to use when connecting through a proxy.
aws-java-sdk-opensdk/src/main/java/com/amazonaws/opensdk/config/ProxyConfiguration.java