I am trying to work out whether there is a way to set up an SFTP server on one machine which provides access to a subset of files on a different SFTP server.
For example /home/global is accessible by the existing SFTP (backend) server with a single user/pass login, but the new (frontend) SFTP server will allow both User1 and User2 to log in, and each of them will only be able to see files in /home/global/one and /home/global/two respectively. All the permissions in /home/global are the same, i.e. access will need to be controlled outside of the filesystem, by the frontend SFTP server, so User2 can't see User1's files (despite them having the same filesystem permissions on the backend server, and being accessed through the same user/pass login to the backend server.)
In effect, I have a single SFTP login I want to split up so different logins are needed to access various areas of the account.
For some background, I have a web hosting account with DreamHost, but they have changed their policy to disallow the sharing of directories between users. This means I will have to give out the username and password of my shell account to any user who needs to upload files, which for me, significantly reduces security. Since I can no longer delegate a subset of my website out to more restrictive user account, I think this is the only option to control shared access.