如何在Node.js中正确调用AWS.CloudFront.Signer?

var AWS = require('aws-sdk');
const fs = require("fs");
var options = { keypairId: 'keypairId', privateKeyPath: 'privateKeyPath', expireTime: (new Date().getTime() + 3000) };
var url = 'cloudfrontURL' + objectpath;
const key = fs.readFileSync('privateKeyPath').toString("ascii");
const id = 'keypairId';
const signer = new AWS.CloudFront.Signer(id, key);
const params = {
	url: url,
	expires: 1538999532,
};
signer.getSignedUrl(params, function (err, data) {
	if (err) { console.log(err) }
	console.log(data);
});