I need to access files from a lot of SSH servers, all of which can only be reached via a jump host. Is it possible to add a SFTP site configuration with jump host(s)? I didn't see such an option in the FTP address book. For more details on SSH jump hosts, see: How to Set Up an SSH Jump Server in Linux (tecmint.com).
Jump hosts are not something we have explicit support for.
FWIW, I have used STunnel with Opus successfully in the past to proxy connections, but I don't know if that would work with your network/firewall environment.
From what I understand, STunnel is an encryption wrapper to add TLS encryption to existing clients and servers. Wouldn't STunnel require me to run it on the jump host as a server? If so, it won't work as we have limited capabilities/permissions on the jump hosts. It's somewhat different from regular SSH tunneling. Missing SSH tunneling capability is the only reason I end up using WinSCP instead of Opus.
SSH server is already setup on the jump host for us, so we have to use only that for further connections.
Snapshot of the setting in WinSCP:
STunnel = SSH Tunnel, so it sounds like we're talking about the same sort of thing, but WinSCP has it built-in while STunnel is a separate thing you can use with almost any SSH/SFTP client.
The way STunnel works (at least when I used it) is you run it on the local machine (although it can be another machine as well, if desired), and configure it so that when you connect to it, it then connects to the SFTP site as a proxy.
(It's a long time since I used it, so I may have the details slightly wrong.)
Like stunnel, we can create the tunnel in windows using the ssh client local port forwarding as ssh -L 2222:destination:22 user@jumphost. After that, I can connect to port 2222 on localhost using DOpus and login using remote server credentials. However, it gets cumbersome to start a local port forwarding when I have 10 or 20 such destinations. It would be great if we could simply specify the jump host in the address book along with rest of connection information. Alternatively you could support the more generic approach of using the SSH config file (%USERPROFILE%\.ssh or %PROGRAMDATA%\ssh\config). We generally specify the connection settings (like address book) in a SSH config file. If DOpus could use the SSH config file, we may be able to support many advanced usages beyond the address book for SCP/(S)FTP over SSH connections.
Does DOpus have an SDK or something (header files and libraries) that I could use to create an advanced SFTP/SCP addon like this? The extension could add another connection type "SCP/SFTP (using SSH Config)" in the FTP address book and then possibly use a different backend to provide the filesystem data over a SSH connection setup using config file and libssh.
CORRECTION: The SSH config file in %USERPROFILE% is %USERPROFILE%\.ssh\config.