core/play-guice/src/main/java/play/inject/guice/GuiceApplicationBuilder.java
public GuiceApplicationBuilder withConfigLoader(Function<Environment, Config> load) {
    return newBuilder(
        delegate.loadConfig(
            func(
                (play.api.Environment env) ->
                    new play.api.Configuration(load.apply(new Environment(env))))));
  }
public GuiceApplicationBuilder withConfigLoader(Function<Environment, Config> load) {
    return newBuilder(
        delegate.loadConfig(
            func(
                (play.api.Environment env) ->
                    new play.api.Configuration(load.apply(new Environment(env))))));
  }
Set the initial configuration loader. Overrides the default or any previously configured
values.

@param load the configuration loader
@return the configured application builder