How to use ssh agent forwarding with “vagrant ssh”?

I’m using vagrant 2 on OS X Mountain Lion.

Vagrant.configure("2") do |config|
  config.ssh.private_key_path = "~/.ssh/id_rsa"
  config.ssh.forward_agent = true
end

1. config.ssh.private_key_path is your local private key
2. Your private key must be available to the local ssh-agent. You can check with ssh-add -L, if it’s not listed add it with ssh-add ~/.ssh/id_rsa
3. Don’t forget to add you public key to ~/.ssh/authorized_keys on the Vagrant VM. You can do it copy-and-pasting or using a tool like ssh-copy-id