docs: function compute_keys(o, opts, req, res) {
  	debug.assert(o).is('object');
  	debug.assert(opts).is('object');
  	ARRAY(Object.keys(opts)).forEach(function(key) {
  		debug.assert(opts[key]).is('function');
  		o[key] = opts[key].call(o, req, res);
  	});
  	return o;
  }