.ssh/config

config

# .ssh/config
# ... other stuff

Host *
  Compression yes
  ForwardAgent yes
  TCPKeepAlive yes
  Protocol 2

deploy.rb

# depot/config/deploy.rb
require 'bundler/capistrano'
# ...

# adjust if you are using RVM, remove if you are not
require "rvm/capistrano"
set :rvm_ruby_string, '1.9.3'
set :rvm_type, :user

ssh_options[:forward_agent] = true # add this

# file paths
set :repository,  "#{user}@#{domain}:git/#{application}.git"
set :deploy_to, "/home/#{user}/#{domain}"

# ...