framework/web/User.php
protected function beforeLogout($identity)
    {
        $event = new UserEvent([
            'identity' => $identity,
        ]);
        $this->trigger(self::EVENT_BEFORE_LOGOUT, $event);

        return $event->isValid;
    }
protected function beforeLogout($identity)
    {
        $event = new UserEvent([
            'identity' => $identity,
        ]);
        $this->trigger(self::EVENT_BEFORE_LOGOUT, $event);

        return $event->isValid;
    }
This method is invoked when calling [[logout()]] to log out a user.
The default implementation will trigger the [[EVENT_BEFORE_LOGOUT]] event.
If you override this method, make sure you call the parent implementation
so that the event is triggered.
@param IdentityInterface $identity the user identity information
@return bool whether the user should continue to be logged out