The $Security.Sessions.Current.ClientVersion can be used to achieve this requirement:
function onPreModify($Request)
{
$Security.Sessions.Refresh()
$ClientSession = ($Security.Sessions.Current.ClientVersion).ToString()
$ClientSession = $ClientSession.SubString(0,13)
$EventLog.ReportEvent($Constants.EDS_EVENTLOG_WARNING_TYPE, "Client is " + $ClientSession)
}
The above script will log the client used to access ARS: