Limit particular AD users on APM?

Here is what I am doing right now, not quite sure if this is a "good" solution, seems a little clunky:

when HTTP_REQUEST {
if { [string length [ACCESS::session data get session.logon.last.username]] > 0 } {
if { ((! [class match [string tolower [ACCESS::session data get session.logon.last.username]]   contains MyDataGroup-acl] )) } {
HTTP::respond 200 content "Please contact XXXXXXX for access to this site."
}
}
}