Flysystem for PHP:
Flysystem is a filesystem abstraction which allows you to easily swap out a local filesystem for a remote one.
A common API for accessing files stored locally, on S3, FTP, SFTP, Dropbox, Rackspace, Zip, and WebDAV. Abstraction layers usually impose a performance penalty, I wonder how big that is in this case. Even with a performance penalty a shared API may be preferred for some situations.