There is a well-established and widely-support IETF standard mechanism (consisting of several IETF standards) for that; it's called WebDAV.
> S3 is probably the closest thing to replacing FTP,
SFTP is much closer to replacing FTP, to the point that people often say FTP when they mean SFTP, which underlies most non-HTTPS enterprise integrations I've seen in the last decade. But SFTP isn't FTP (not even FTP-over-TLS, which is FTPS, which has much less use.)
> Ftp is surprisingly common when integrating between parties
SFTP is very common. FTP (including FTPS) is surprisingly common in the sense that any use of it is surprising given the well-established, battle tested, and superior in every way alternatives that are readily available.
There is a well-established and widely-support IETF standard mechanism (consisting of several IETF standards) for that; it's called WebDAV.
> S3 is probably the closest thing to replacing FTP,
SFTP is much closer to replacing FTP, to the point that people often say FTP when they mean SFTP, which underlies most non-HTTPS enterprise integrations I've seen in the last decade. But SFTP isn't FTP (not even FTP-over-TLS, which is FTPS, which has much less use.)
> Ftp is surprisingly common when integrating between parties
SFTP is very common. FTP (including FTPS) is surprisingly common in the sense that any use of it is surprising given the well-established, battle tested, and superior in every way alternatives that are readily available.