title: Dialogflow custom authentication
body: <p>I have an iOS app that connects to dialogflow agent.  The dialogflow agent uses google cloud functions to fulfill the users request. </p>
  
  <p>In the iOS app I’m using Firebase authentication to authenticate the user.  I would like to include the Firebase idtoken in the dialogflow request so that I can access the idtoken In the cloud function. Is this possible? If so how could I achieve this? </p>
  
  <p>Thanks in advance </p>