Copy public key to .ssh/authorized_keys inside Vagrant vm:
Vagrant.configure("2") do |config|
config.vm.provision "file", source: "~/.ssh/id_rsa.pub", destination: "~/.ssh/authorized_keys"
config.ssh.private_key_path = ["~/.vagrant.d/insecure_private_key", "~/.ssh/id_rsa"]
config.ssh.insert_key = false
end
``