let one user can log-in only one instance.

[retsyo]

code snippet

I found that we can use one same user/password to log-in nicegui-main\examples\authentication\main.py multi-times at same time. So I made some changes to forbide the beheviour

please note, we have to delete username.value from lstLoggedUser in log out function, which is not included here

lstLoggedUser = []

@ui.page('/login')
def login() -> Optional[RedirectResponse]:
    def try_login() -> None:  # local function to avoid passing username and password as arguments
        if passwords.get(username.value) == password.value:
            if username.value not in lstLoggedUser:
                lstLoggedUser.append(username.value)

                app.storage.user.update({'username': username.value, 'authenticated': True})
                ui.open(app.storage.user.get('referrer_path', '/'))  # go back to where the user wanted to go
            else:
                ui.notify('you have already logged in', color='negative')