如何把会员名写入日志

apache的日志有个%u参数，意思为远程用户（来自auth；如果返回状态（%s）是401则可能是伪造的）。请问如何把我网站的会员名一同写入日志呢？
普通标准的日志格式：
211.147.215.250 － － [13/Apr/2008:00:12:40 +0800] "GET / HTTP/1.1" 200 2747 "-" "Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; .NET CLR 2.0.50727; .NET CLR1.1.4322; .NET CLR 3.0.04506.30)"
我希望的日志格式：
211.147.215.250 - aaa [13/Apr/2008:00:12:40 +0800] "GET / HTTP/1.1" 200 2747 "-" "Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; .NET CLR 2.0.50727; .NET CLR1.1.4322; .NET CLR 3.0.04506.30)"

211.147.215.250 - bbb [13/Apr/2008:00:12:40 +0800] "GET / HTTP/1.1" 200 2747 "-" "Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; .NET CLR 2.0.50727; .NET CLR1.1.4322; .NET CLR 3.0.04506.30)"