The following code can be used on your site to list all the attributes and values stored in the Request object. It's wrapped with a condition to only display when debug=true has been set in the URL as a parameter.
#if($request.getParameter("debug"))
<h3>HTTP Request Attributes</h3>
#set($reqAttrList = $request.getAttributeNames())
#foreach($reqAttr in $reqAttrList)
<br/>Attr = $reqAttr Value = $request.getAttribute($reqAttr)
#end
#end