alternative to authUrl to pass in promise of auth token request

[smblee]

hello, I would love an option to pass in a new onAuthRequest prop or change the authCallback to accept async functions

new Ably.Realtime({
  onAuthRequest: async () => { 
    await ensureAuthRefreshed();
    const res = await myApiClient.getAblyToken();

   return res.result.data;
  }
})

I think the current authCallback is super limited/clunky since its only synchronous.

This would also allow for ease of use for people who use trpc since it by default returns a nested data shape (res.result.data.json would be where the result is stored).

Issue is synchronized with this Jira Task by Unito

[smblee]

For now as a hacky workaround I had to make a custom patch to ably-js like so to access the proper data, but I am still unable to make extra calls such as await ensureAuthRefreshed()

[lawrence-forooghian]

Hi @smblee, thanks for raising this issue! I'd like to understand a bit better what is the issue that you're facing and why you've had to modify the ably-js library code.

I agree with you that the current authCallback mechanism is a bit clunky to use when the underlying user-defined mechanism for fetching an Ably token uses async functions. We have #1360 which suggests improving this experience. But, whilst clunky, it is possible to bridge the authCallback mechanism with an async mechanism using the Promise API, for example:

new Ably.Realtime({
  authCallback: (tokenParams, callback) => {
    const ablyTokenPromise = (async () => {
      // The body of this function is copied from your suggestion
      await ensureAuthRefreshed();
      const res = await myApiClient.getAblyToken();

      return res.result.data; // I'm assuming that res.result.data is an Ably token as either an Ably.TokenDetails or a string
    })();

    ablyTokenPromise.then((ablyToken) => {
      callback(null, ablyToken);
    }).catch((error) => {
      callback(error, null);
    });
  }
});

But, since you needed to modify the Ably library code, it seems like there's some other element to this issue that I haven't properly understood yet. Please could you explain a bit more about what it is that you're trying to achieve with this library change?

[smblee]

ahhh i didnt realize the second "callback" argument did that! that actually would work. yes clunky but it should be good for now. lemme give that a try and report back

[smblee]

ok can confirm this works for my use case. Would be cool to document this somewhere for others with the same use case :)

[lawrence-forooghian]

Thanks for confirming that it worked! We do already document the fact that the second argument to authCallback is a completion handler; e.g. https://ably.com/docs/auth/token#auth-callback (although I'm not sure why it says async on the authCallback in that example, it's a bit confusing, will get that fixed!)

[lawrence-forooghian]

(Actually just realised there's nothing wrong with that example, even though it's a bit confusing to mix code that uses callbacks and promises.)