signed-url.js

const express = require('express')
const app = express()

const AWS = require('aws-sdk')
const s3 = new AWS.S3()

const signedUrlExpireSeconds = 60 * 5
const bucket = 'mf-uploads'


app.post('/signed-url', (req, res) => {
  // req.body.method = 'getObject' for download url or 'putObject' for upload url
  const url = s3.getSignedUrl(req.body.method, {
      Bucket: bucket,
      Key: req.body.filename,
      Expires: signedUrlExpireSeconds
  })
  res.json({ url })
})