How to store API Keys in node process?

app.js

// ./app.js
// My GitHub API credentials are all hardcoded in a credentials.js file
var credentials = require('./credentials');
var GITHUB_CLIENT_ID = credentials.github.id;
var GITHUB_CLIENT_SECRET = credentials.github.secret;
var CALLBACK_URL = credentials.github.callback;

credentials.js

// ./credentials.js
// This file is in .gitignore so we don't check in any these keys.

module.exports = {
  github: {
    id: 'GITHUB_ID',
    secret: 'GITHUB_SECRET',
    callback: 'http://127.0.0.1:3000/auth/github/callback'
  }
  // other API Keys here; truncated for length.
};