title: fb login doesn't ask for credentials for login even after logging out iOS swift 4
body: <p>I am implementing fb login in iOS app, want to login using different fb accounts in same app.</p>
  
  <p>I've installed sdk using cocoapods and not using any third party library. swift 4, Xcode 9, </p>
  
  <p>let manager = LoginManager()</p>
  
  <pre><code>func loginButton(_ loginButton: FBLoginButton, didCompleteWith result: LoginManagerLoginResult?, error: Error?) {
  
      if (AccessToken.current == nil){
      //loginButton.loginBehavior = .browser
      DispatchQueue.main.async(){
    // LoginManager.init(loginBehavior: .web, defaultAudience: .everyone)
  
          print(LoginBehavior.self)
      self.manager.logIn( permissions: [ .publicProfile, .email ], viewController: self){(result) in
          switch result {
          case .cancelled:
              print("user cancelled login process")
              break
          case .failed(let err):
              print("login failed with error: \(err.localizedDescription)")
              break
          case .success(let grantedPermissions, let declinedPermissions, let accessToken):
              print(accessToken)
            //get user profile
  
  
          }
      }
      }
      print("login")
      } else {
          print("user is already Logged in")
      }
  }
  func loginButtonDidLogOut(_ loginButton: FBLoginButton) {
      AccessToken.current = nil
      manager.logOut()
  }
  </code></pre>
  
  <p>I can login and logout. but it doesn't ask me to enter password next time I try to login. means I can not login using different fb account.</p>
  
  <p>also in AppDelegate file I am getting error implementing fbsdk functions:</p>
  
  <pre><code>func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -&gt; Bool {
  
       SDKApplicationDelegate.shared.application(application, didFinishLaunchingWithOptions: launchOptions) 
       return true
  }
  
  func application(_ app: UIApplication, open url: URL, options: [UIApplication.OpenURLOptionsKey : Any] = [:]) -&gt; Bool {
     return SDKApplicationDelegate.shared.application(app, open: url, options: options)
  
     }
  </code></pre>