For an HTTPS proxy you can use ProxyTunnel (you may also need to get the SSH server listening on port 443 as most HTTPS proxies forbid connections to port 22). For a SOCKS4/SOCKS5 proxy (unlikely) you can use socat.

In any case, first find the particular ProxyCommand directive that allows OpenSSH to connect to the remote server through the proxy using any of these utilities.

Then, pass it to Net::SFTP::Foreign on the constructor call as follows:

my $sftp = Net::SFTP::Foreign->new(..., more => [-o => 'ProxyCommand=.
+..']);
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