How to use external .groovy config file in Grails 3

I found this thread and quotation by Graeme Rocher:

Grails 3 uses Spring's property sources concept, so it will resolve properties from the system, the environment and finally the application.yml/application.groovy

and code by Clyde Balneaves:

class Application extends GrailsAutoConfiguration implements EnvironmentAware {
    static void main(String[] args) {
    GrailsApp.run(Application)
    }

    @Override
    void setEnvironment(Environment environment) {
    //Set up Configuration directory
    def krakenHome = System.getenv('KRAKEN_HOME') ?: System.getProperty('KRAKEN_HOME') ?: "/opt/kraken"

    println ""
    println "Loading configuration from ${krakenHome}"
    def appConfigured = new File(krakenHome, 'KrakenConfig.groovy').exists()
    println "Loading configuration file ${new File(krakenHome, 'KrakenConfig.groovy')}"
    println "Config file found : " + appConfigured

    if (appConfigured) {
        def config = new ConfigSlurper().parse(new File(krakenHome, 'KrakenConfig.groovy').toURL())
        environment.propertySources.addFirst(new MapPropertySource("KrakenConfig", config))
    }
    }
}