This is a AWS S3 secure redirect to a file

redirect.js

// secureRedirect redirects this fileId to be loaded directly from S3.
// if filename is provided, it will trigger a download of that filename
export function secureRedirect({ reply, fileId, filename }) {
  const key = makeS3Key(fileId);
  let contentDisposition;
  if (filename && Buffer.from(filename, 'utf8').toString('ascii') === filename) {
    contentDisposition = `attachment; filename="${filename}"`;
  } else if (filename) {
    const encodedFilename = Querystring.escape(filename);
    contentDisposition = `attachment; filename*=UTF-8''${encodedFilename}`;
  }

  const url = S3.getSignedUrl('getObject', {
    Bucket: BUCKET,
    Key: key,
    Expires: Math.floor(FilesConfig.expiresInMillis / 1000),
    ResponseContentDisposition: contentDisposition,
  });

  return reply().redirect(url);
}