暂时自己实现了一个类如下：

namespace App\Services;

use Monolog\Logger;
use Monolog\Handler\RotatingFileHandler;
use Monolog\Processor\WebProcessor;
use Monolog\Processor\MemoryUsageProcessor;
use Monolog\Formatter\LineFormatter;
use Request;
use Sentry;
use Config;
use Auth;

/**
 * UserLog
 *
 * Custom monolog logger for CMS user : DEBUG,INFO,NOTICE,WARNING,ERROR,CRITICAL,ALERT,EMERGENCY
 *
 * @author     
 */ 
class UserLog {

    /**
     * write 
     * @return void
     */
    public static function debug($log)
    {
        self::write($log,Logger::DEBUG);
    }
    public static function info($log)
    {
        self::write($log,Logger::INFO);
    }
    public static function notice($log)
    {
        self::write($log,Logger::NOTICE);
    }
    public static function warning($log)
    {
        self::write($log,Logger::WARNING);
    }
    public static function error($log)
    {
        self::write($log,Logger::ERROR);
    }
    public static function critical($log)
    {
        self::write($log,Logger::CRITICAL);
    }
    public static function alert($log)
    {
        self::write($log,Logger::ALERT);
    }
    public static function emergency($log)
    {
        self::write($log,Logger::EMERGENCY);
    }

    private static function write($logtext='',$level=Logger::INFO)
    {
        if ("yes"==Config::get('app.userlog')) 
        {
            $log = new Logger('userlog');
            // handler init, making days separated logs
            $handler = new RotatingFileHandler(Config::get('app.userlog_path'), 0, $level);        
            // formatter, ordering log rows
            $handler->setFormatter(new LineFormatter("[%datetime%] %channel%.%level_name%: %message% %extra% %context%\n"));
            // add handler to the logger
            $log->pushHandler($handler);
            // processor, adding URI, IP address etc. to the log
            $log->pushProcessor(new WebProcessor);
            // processor, memory usage
            $log->pushProcessor(new MemoryUsageProcessor);

            $userinfo=" [] ";
            $user = Auth::user();
            if($user)
            {
                $userinfo=' [USERID:'.$user->id.'] ';
            }

            $log->addInfo($logtext.$userinfo);        
        }
    }
}

用的时候，就是直接 UserLog.info("log here");
默认会记录到storage/app下，但是要在app.php里增加两个配置项：

'userlog'=>env('USER_LOG', 'yes'),

    'userlog_path'=>env('USER_LOG_PATH', storage_path().'/logs/useractivity.log'),