swift - FirebaseUI iOS remove cancel button -

i'm new in ios development. wanna build authorization firebase. i'm using firebaseui-ios. wanna hide cancel button initial screen. have ideas how it?

i create firebase authviewcontroller programmatically:

import uikit import firebase import firebaseauthui import firebasegoogleauthui  class authviewcontroller: uiviewcontroller {  fileprivate var _authhandle: firauthstatedidchangelistenerhandle! var user: firuser?  override func viewdidload() {     super.viewdidload()     configureauth() }  func configureauth() {     let provider: [fuiauthprovider] = [fuigoogleauth()]     fuiauth.defaultauthui()?.providers = provider     fuiauth.defaultauthui()?.issigninwithemailhidden = true      // listen changes in authorization state     _authhandle = firauth.auth()?.addstatedidchangelistener { (auth: firauth, user: firuser?) in         // check if there current user         if let activeuser = user {             // check if current app user current firuser             if self.user != activeuser {                 self.user = activeuser                 let name = user!.email!.components(separatedby: "@")[0]                 print(name)             }         } else {             // user must sign in             self.loginsession()         }     } }  func loginsession() {     let authviewcontroller = fuiauth.defaultauthui()!.authviewcontroller()     present(authviewcontroller, animated: true, completion: nil) }  deinit {     firauth.auth()?.removestatedidchangelistener(_authhandle) } } 

for can set leftbarbuttonitem nil in viewdidload or in viewwillappear.

self.navigationitem.leftbarbuttonitem = nil