Auth0 Flutter Integration

I followed this tutorial to integrate Auth0 with my flutter app to get roles for users:

The code provided uses the clientCredentialsGrant function, when trying to login it fails and the logs show: auth0.clientCredentialsGrantRequest is not a function.
Looking at the current nodeJS docs shows that the function indeed does not exist, but the other two clientcredentialsgrant functions also throw the same error in the logs.
Clearly the tutorial is out of date, so what should I be using instead to assign roles to users?