title: How to obtain trigger_id from Slack's Slash Commands?
body: <p>I've successfully been able to create a basic slash command but the request body (sent from Slack triggered upon the slash command) does not include a <code>trigger_id</code>.  How do I obtain this <code>trigger_id</code>?  Apparently, I need this in order to generate a Slack dialog which is my ultimate goal. </p>
  
  <p>The response looks something like this: </p>
  
  <pre><code>{ token: 'MY_TOKEN',
    team_id: 'MY_TEAM_ID',
    team_domain: 'testing',
    channel_id: 'D0JPDEPN5',
    channel_name: 'directmessage',
    user_id: 'U0JPD5E07',
    user_name: 'ryan',
    command: '/testcommand',
    text: '',
    response_url: 'https://hooks.slack.com/commands/T0JP043M/3884242426501/bPgV4224Kflxhh6mmNF1O0YHp5' }
  </code></pre>
  
  <p>No <code>trigger_id</code> to be found. </p>