title: Can I add an expiry date to a customToken with Firebase v3?
body: <p>I am in the process of migrating a node.js application to Firebase v3.</p>
  
  <p>In v2 I was using <a href="https://github.com/firebase/firebase-token-generator-node" rel="noreferrer">FirebaseTokenGenerator</a> to generate custom tokens. It requires an apiToken, which is inconsistent with the way that Firebase v3 works in node, and I see there is now a '<a href="https://firebase.google.com/docs/reference/node/firebase.auth.Auth#property" rel="noreferrer">createCustomToken</a>' method on the firebase.auth service so I am assuming that I should now use that.</p>
  
  <p>The issue is that this method appears to accept only 'uid' and 'developerClaims' as parameters, where FirebaseTokenGenerator also accepted an options object which included an 'expires' attribute.</p>
  
  <p>Is there a way to give the token generated by 'createCustomToken' an expiry date?</p>