public static function settings_fields( $fields = array() ) {

		foreach ( self::$integrations as $key => $integration ) {
			if ( ! ( $integration instanceof PUM_Interface_Integration_Settings ) || ! $integration->enabled() ) {
				continue;
			}

			// TODO LEFT OFF HERE.
			// TODO Could this be done via add_filter( 'pum_settings_fields', array( $integration, 'append_fields' ) );
			// TODO If so, do we do it inside the __construct for the PUM_Abstract_Integration, or the Integration_{Provider} class itself.
			// TODO Alternatively do we simply loop over all enabled providers during self::init() and add the filters/hooks there instead.
			$fields = $integration->append_fields( $fields );
		}

		return $fields;
	}