@Override
    public void shutdown() {
        if (authProvider != null)
            authProvider.shutdown();
    }
Logs a warning that the authentication process will be entirely aborted
due to an internal error, advising the administrator to set the
"skip-if-unavailable" property if error encountered is expected and
should be tolerated.
guacamole/src/main/java/org/apache/guacamole/extension/AuthenticationProviderFacade.java