# File lib/chef/rest/auth_credentials.rb, line 41
      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
        request_params[:proto_version] = Chef::Config[:authentication_protocol_version]
        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