AgoraVideoViewController.swift

var inCall = false
let tempToken: String? = nil //If you have a token, put it here.
var callID: UInt = 0 //This tells Agora to generate an id for you. We have user IDs from Firebase, but they aren't Ints, and therefore won't work with Agora.
var channelName: String?

override func viewWillAppear(_ animated: Bool) {
    handle = Auth.auth().addStateDidChangeListener { (auth, user) in
        self.currentUser = user
        if user == nil {
            self.showFUIAuthScreen()
        } else {
            self.joinChannel(channelName: user!.uid)
        }
    }
}

func joinChannel(channelName: String) {
    getAgoraEngine().joinChannel(byToken: tempToken, channelId: channelName, info: nil, uid: callID) { [weak self] (sid, uid, elapsed) in
        self?.inCall = true
        self?.callID = uid
        self?.channelName = channelName
    }
}