iRule to Allow Outlook users by Username

I think i may have figured it out. After spending some hours looking at packet captures I noticed in the URI active sync always sends the username as part of the string. So using an iRule it searches that URI for the specific user identity and if it matches, it lets it through. Seems to be working so for but have yet to do extensive testing on it. I just wonder how bad the resource usage on the F5s will be having to inspect the URI of every connection. Thanks for the replies!

    "/Microsoft-Server-ActiveSync*" {
       if { [HTTP::uri] contains "username"}{
        persist cookie
        pool POOL
        }
        else {
                     discard
        }