Capistrano deploy via gateway host

gateway_deploy.rb

set :user, 'username'
set :gateway, 'example.com'

set :ssh_options, {
  user: fetch(:user),
  forward_agent: false,
  proxy: Net::SSH::Proxy::Command.new(
    "ssh -l #{fetch(:user)} #{fetch(:gateway)} -W %h:%p"
  )
}