s3.getSignedUrl('putObject', { Key: userProvidedSha256 }, callback)

const signPostFile = () => {
  const params = {
    Fields: {
      key: userProvidedSha256
    },
    Expires: 86400,
    Conditions: [
      ['content-length-range', 0, 10000000],
      { 'X-Amz-Content-Sha256': userProvidedSha256]
    ]
  }

  s3.createPresignedPost(params, callback)
}

----------------------------986452911605138616518063
Content-Disposition: form-data; name="X-Amz-Content-Sha256"

b94d27b9934d3e08a52e52d7da7dabfac484efe37a5380ee9088f7ace2efcde9
----------------------------986452911605138616518063
Content-Disposition: form-data; name="key"

b94d27b9934d3e08a52e52d7da7dabfac484efe37a5380ee9088f7ace2efcde9

const s3 = new AWS.S3({apiVersion: '2006-03-01', signatureVersion: 'v4'});