I am doing R&D on how to implement a pubnub access manager in swift, and after some research, I come to know :
The PubNub Swift SDK (Access Manager Tutorial) does not have grant method because you need to init PubNub with your secret key and you should never do so in a client application. You should only do so in a secure server. Your server grants permissions to an auth-key that is passed back to your clients, like a Swift app, and that auth-key is used to init PubNub with your subscribe key and optionally your publish key.