Generate File Upload policy for Amazon s3

amazon-s3-upload.js

'use strict';
var AWS = require('aws-sdk'),
    crypto = require('crypto'),
    createS3Policy,
    getExpiryTime;

getExpiryTime = function () {
    var _date = new Date();
    return '' + (_date.getFullYear()) + '-' + (_date.getMonth() + 1) + '-' +
        (_date.getDate() + 1) + 'T' + (_date.getHours() + 3) + ':' + '00:00.000Z';
};

createS3Policy = function(contentType, subFolder, callback) {
    var s3Policy = {
		'expiration': getExpiryTime(),
        'conditions': [
            ['starts-with', '$key', subFolder],
            {'bucket': 'nba-agc'},
            {'acl': 'public-read'},
            ['starts-with', '$Content-Type', contentType]
        ]
    };
	// stringify and encode the policy
    var stringPolicy = JSON.stringify(s3Policy);
    var base64Policy = new Buffer(stringPolicy, 'utf-8').toString('base64');
	
	// sign the base64 encoded policy
    var signature = crypto.createHmac('sha1', process.env.AWS_SECRET_KEY)
        .update(new Buffer(base64Policy, 'utf-8')).digest('base64');
	
	// build the results object
    var s3Credentials = {
        s3Policy: base64Policy,
        s3Signature: signature,
        AWSAccessKeyId: process.env.AWS_ACCESS_KEY_ID
    };
	
	// send it back
    callback(s3Credentials);
};

/*
 * Later, we can then use the preceeding methods in a request handler
 */
app.get('/s3_policy', function(req, res) {
    createS3Policy(req.query.mimeType, req.query.subFolder, function (creds, err) {
        if (!err) {
            return res.send(200, creds);
        } else {
            return res.send(500, err);
        }
    });
});