Function connect_with_tunnel 

pub fn connect_with_tunnel(
    url: &DatabaseUrl,
    opts: &ConnectOptions,
    ssh_config: &SshConfig,
    key_source: &KeySource,
    proxy: Option<&ProxyConfig>,
) -> Result<Box<dyn Connection>, SqlError>

Establish a blocking connection to url through an SSH tunnel.

An optional proxy routes the SSH session itself through an HTTP CONNECT proxy. See connect for the runtime / blocking contract: the returned handle owns the private runtime that also hosts the SSH session and (for the LocalListener transport) the byte-forwarder task, so all of them are driven on every later blocking call and torn down together when the handle drops.