code: function token_options (post_data) {
    return {
      body: post_data, // see make_post_data above
      headers: {
        'Accept': 'application/json',
        'Content-Type': 'application/x-www-form-urlencoded',
        'Content-Length': post_data.length
      },
      hostname: process.env.GITHUB_HOSTNAME || 'github.com',
      method: 'POST',
      path: '/login/oauth/access_token',
      port: 443
    };
  }
docs: http.request options for requesting the OAuth2 token
  see: developer.github.com/v3/oauth/#github-redirects-back-to-your-site
  @param {String} post_data the POST data we are sending to GitHub
  @returns {Object} data & headers we are sending to GitHub in our HTTP request