I bet you could do this with split. I don't see many people taking advantage of its regex engine:

($client,$identuser,$authuser,$date,$tz,$method,
    $url,$protocol,$status,$bytes,$refer,$platform,$extendedinfo) =
        split(/[\[\]"]?\s[\[\]"]?/, 13);
[download]

Hmm, it leaves a quote sign on the extended info. Pretty close, though.