Firebase no iOS: avaliando a necessidade de atualização manual de tokens

Atualmente, estou usando o seguinte código no meu cliente iOS para determinar se precisamos apresentar uma tela de login:

if Auth.auth().currentUser == nil

Aqui está a lógica da tela de login:

      @objc func handleAppleSignUp() {
          Analytics.logEvent("handleAppleSignUp", parameters: nil)
          
          appleSignUpButton?.stopPulseAnimation()
          
          startSignInWithAppleFlow()
      }

      //
      // https://firebase.google.com/docs/auth/ios/apple
      //
      
      @available(iOS 13, *)
      func startSignInWithAppleFlow() {
        let nonce = randomNonceString()
        currentNonce = nonce
        let appleIDProvider = ASAuthorizationAppleIDProvider()
        let request = appleIDProvider.createRequest()
        request.requestedScopes = [.fullName, .email]
        request.nonce = sha256(nonce)

        let authorizationController = ASAuthorizationController(authorizationRequests: [request])
        authorizationController.delegate = self
        authorizationController.presentationContextProvider = self
        authorizationController.performRequests()
      }
      
      private func randomNonceString(length: Int = 32) -> String {
        precondition(length > 0)
        var randomBytes = [UInt8](repeating: 0, count: length)
        let errorCode = SecRandomCopyBytes(kSecRandomDefault, randomBytes.count, &randomBytes)
        if errorCode != errSecSuccess {
          fatalError(
            "Unable to generate nonce. SecRandomCopyBytes failed with OSStatus \(errorCode)"
          )
        }

        let charset: [Character] =
          Array("0123456789ABCDEFGHIJKLMNOPQRSTUVXYZabcdefghijklmnopqrstuvwxyz-._")

        let nonce = randomBytes.map { byte in
          // Pick a random character from the set, wrapping around if needed.
          charset[Int(byte) % charset.count]
        }

        return String(nonce)
      }

      @available(iOS 13, *)
      private func sha256(_ input: String) -> String {
        let inputData = Data(input.utf8)
        let hashedData = SHA256.hash(data: inputData)
        let hashString = hashedData.compactMap {
          String(format: "%02x", $0)
        }.joined()

        return hashString
      }
  }

  // https://fluffy.es/sign-in-with-apple-tutorial-ios/
  extension LoginViewController:  ASAuthorizationControllerPresentationContextProviding {
      func presentationAnchor(for controller: ASAuthorizationController) -> ASPresentationAnchor {
          // Return the window of the current view controller
          return self.view.window!
      }
  }

  extension LoginViewController: ASAuthorizationControllerDelegate {
      func authorizationController(controller: ASAuthorizationController, didCompleteWithAuthorization authorization: ASAuthorization) {
        if let appleIDCredential = authorization.credential as? ASAuthorizationAppleIDCredential {
          guard let nonce = currentNonce else {
            fatalError("Invalid state: A login callback was received, but no login request was sent.")
          }
          guard let appleIDToken = appleIDCredential.identityToken else {
            print("Unable to fetch identity token")
            return
          }
          guard let idTokenString = String(data: appleIDToken, encoding: .utf8) else {
            print("Unable to serialize token string from data: \(appleIDToken.debugDescription)")
            return
          }
          // Initialize a Firebase credential, including the user's full name.
          let credential = OAuthProvider.appleCredential(withIDToken: idTokenString,
                                                            rawNonce: nonce,
                                                            fullName: appleIDCredential.fullName)
            
          EmulatorUtils.authUseEmulatorIfPossible()
          
          // Sign in with Firebase.
          Auth.auth().signIn(with: credential) { (authResult, error) in
            if let error = error {
              // Error. If error.code == .MissingOrInvalidNonce, make sure
              // you're sending the SHA256-hashed nonce as a hex string with
              // your request to Apple.
              print(error.localizedDescription)
              return
            }
            // User is signed in to Firebase with Apple.
            // ...
              
              Analytics.logEvent("sign_in_success", parameters: nil)
              
              self.delegate?.updateBasedOnLoginStatus()
          }
        }
      }

      func authorizationController(controller: ASAuthorizationController, didCompleteWithError error: Error) {
        // Handle error.
        print("Sign in with Apple errored: \(error)")
      }
  }

Eu estava pensando: será que precisamos atualizar o token de login manualmente? Alguns dos meus usuários relataram que as interações com o Firebase Functions e o Firestore às vezes falham. Em todos os casos, esse problema é resolvido saindo e entrando novamente.

Se eu precisar atualizar o token de login manualmente, alguém pode explicar como e quando fazer isso?