async def sign_in(self, event=None):
        """
        Note the `event` argument. This is required since this callback
        may be called from a ``widget.bind`` (such as ``'<Return>'``),
        which sends information about the event we don't care about.

        This callback logs out if authorized, signs in if a code was
        sent or a bot token is input, or sends the code otherwise.
        """
        self.sign_in_label.configure(text='Working...')
        self.sign_in_entry.configure(state=tkinter.DISABLED)
        if await self.cl.is_user_authorized():
            await self.cl.log_out()
            self.destroy()
            return

        value = self.sign_in_entry.get().strip()
        if self.code:
            self.set_signed_in(await self.cl.sign_in(code=value))
        elif ':' in value:
            self.set_signed_in(await self.cl.sign_in(bot_token=value))
        else:
            self.code = await self.cl.send_code_request(value)
            self.sign_in_label.configure(text='Code:')
            self.sign_in_entry.configure(state=tkinter.NORMAL)
            self.sign_in_entry.delete(0, tkinter.END)
            self.sign_in_entry.focus()
            return