How to add pem files to target in flightplan automated deployment script for nodejs applications

I am new to node applications deployment, I am using flightplan.js for automated deployments, however in most of the documents I have seen it is only about password less deployments where a user's key is added to server, I want to set up the target where I can specify the location of pem file in order to login to the server, is there a way to do that? right now the target looks like this

    plan.target('staging', [
  {
    host: 'xxx.xxx.xxx',
    username: username,
    agent: process.env.SSH_AUTH_SOCK
  }
]);

I would like to have something where I can pass the pem file path as well, something like this

plan.target('staging', [
  {
    host: 'xxx.xxx.xxx',
    username: username,
    key: PATH_TO_KEY
    agent: process.env.SSH_AUTH_SOCK
  }
]);

You can add your pem files like this,

plan.target('staging', [
  {
    host: 'xxx.xxx.xxx',
    username: username,
    privateKey: 'path/to/file/key.pem',
    agent: process.env.SSH_AUTH_SOCK
  }
]);