    # File lib/chef/rest/auth_credentials.rb, line 40
          def signature_headers(request_params={})
            raise ArgumentError, "Cannot sign the request without a client name, check that :node_name is assigned" if client_name.nil?
            Chef::Log.debug("Signing the request as #{client_name}")

            # params_in = {:http_method => :GET, :path => "/clients", :body => "", :host => "localhost"}
            request_params             = request_params.dup
            request_params[:timestamp] = Time.now.utc.iso8601
            request_params[:user_id]   = client_name
            host = request_params.delete(:host) || "localhost"

            sign_obj = Mixlib::Authentication::SignedHeaderAuth.signing_object(request_params)
            signed =  sign_obj.sign(key).merge({:host => host})
            signed.inject({}){|memo, kv| memo["#{kv[0].to_s.upcase}"] = kv[1];memo}
          end