Providing Custom Handler, Internal Endpoint Still Calls

[olan-go2]

Do you want to request a feature or report a bug?
bug

What is the current behavior?
Providing customHandler for user authentication still fires the endpoint to /pusher/auth

If the current behavior is a bug, please provide the steps to reproduce and
if possible a minimal demo of the problem via https://jsfiddle.net or similar.
Just provider a customHandler

What is the expected behavior?
When providing a customHandler for user authentication, it should not call the internal call to ``/pusher/auth`

Which versions of Pusher, and which browsers / OS are affected by this issue?
Did this work in previous versions of Pusher? If so, which?
^8.4.0-rc2