Private Repository Deployment. As seen at http://fiznool.com/blog/2015/05/20/an-alternative-to-npm-private-modules/

cleanup-ssh.sh

#!/bin/bash
if [ "$GIT_SSH_KEY" != "" ]; then
  echo "Cleaning up SSH config" >&1
  echo "" >&1

  # Now that npm has finished running,
  # we shouldn't need the ssh key/config anymore.
  # Remove the files that we created.
  rm -f ~/.ssh/config
  rm -f ~/.ssh/deploy_key

  # Clear that sensitive key data from the environment
  export GIT_SSH_KEY=0
fi

setup-ssh.sh

#!/bin/bash
if [ "$GIT_SSH_KEY" != "" ]; then
  echo "Detected SSH key for git. Adding SSH config" >&1
  echo "" >&1

  # Ensure we have the ssh folder
  if [ ! -d ~/.ssh ]; then
    mkdir -p ~/.ssh
    chmod 700 ~/.ssh
  fi

  # Load the private key into a file.
  echo $GIT_SSH_KEY | base64 --decode > ~/.ssh/deploy_key

  # Change the permissions on the file to
  # be read-write for this user.
  chmod 600 ~/.ssh/deploy_key

  # Setup the ssh config file.
  # Switch out the hostname for different hosts.
  echo -e "Host github.com\n"\
          " IdentityFile ~/.ssh/deploy_key\n"\
          " IdentitiesOnly yes\n"\
          " UserKnownHostsFile=/dev/null\n"\
          " StrictHostKeyChecking no"\
          > ~/.ssh/config
fi