Hi Alan - did you get this resolved? What technologies will they be using and what are the authentication needs? Blob storage supports upload via HTTP/HTTPS (but not FTP, as stated by others), and you can use the account's keys to auth, or create
more specific permissions to grant to your users. As other stated, you could create a proxy service if you truly need FTP.
Let us know how we can help, sorry for the delay.
-Jeff