Loop through Request object keys

This works to loop through all Form keys:

foreach (string s in Request.Form.Keys )        
        {       
            Response.Write(s.ToString() + ":" + Request.Form[s] + "<br>");      
        }

But, I want to loop through all Request keys:

foreach (string s in Request )      
        {       
            Response.Write(s.ToString() + ":" + Request[s] + "<br>");       
        }

Problem is request.keys is not a collection. But clearly the request object has children that I want to loop through. I'm pretty sure it's possible, I'm just using bad syntax.

thanks in advance!