### SSH key pair automation

The VirtualBox builders can inject the current SSH key pair's public key into
the template using the following variable:

-   `SSHPublicKey` (*VirtualBox builders only*) - This is the SSH public key
    as a line in OpenSSH authorized_keys format.

When a private key is provided using `ssh_private_key_file`, the key's
corresponding public key can be accessed using the above variables.

If `ssh_password` and `ssh_private_key_file` are not specified, Packer will
automatically generate en ephemeral key pair. The key pair's public key can
be accessed using the template variables.

For example, the public key can be provided in the boot command as a URL
encoded string by appending `| urlquery` to the variable:

```json
{
    "type": "virtualbox-iso",
    "boot_command": [
      "<up><wait><tab> text ks=http://{{ .HTTPIP }}:{{ .HTTPPort }}/ks.cfg PACKER_USER={{ user `username` }} PACKER_AUTHORIZED_KEY={{ .SSHPublicKey | urlquery }}<enter>"
    ]
}
```

A kickstart could then leverage those fields from the kernel command line by
decoding the URL-encoded public key:

``` sh
%post

# Newly created users need the file/folder framework for SSH key authentication.
umask 0077
mkdir /etc/skel/.ssh
touch /etc/skel/.ssh/authorized_keys

# Loop over the command line. Set interesting variables.
for x in $(cat /proc/cmdline)
do
  case $x in
    PACKER_USER=*)
      PACKER_USER="${x#*=}"
      ;;
    PACKER_AUTHORIZED_KEY=*)
      # URL decode $encoded into $PACKER_AUTHORIZED_KEY
      encoded=$(echo "${x#*=}" | tr '+' ' ')
      printf -v PACKER_AUTHORIZED_KEY '%b' "${encoded//%/\\x}"
      ;;
  esac
done

# Create/configure packer user, if any.
if [ -n "$PACKER_USER" ]
then
  useradd $PACKER_USER
  echo "%$PACKER_USER ALL=(ALL) NOPASSWD: ALL" >> /etc/sudoers.d/$PACKER_USER
  [ -n "$PACKER_AUTHORIZED_KEY" ] && echo $PACKER_AUTHORIZED_KEY >> $(eval echo ~"$PACKER_USER")/.ssh/authorized_keys
fi

%end
```