When you are online, the integrated LED (PIN2 in the WemOS D1 mini) will be on. When on captive portal LED will be blinking. When offline LED will be off.
Open the main.py file and enter your WiFi credentials there. Maybe you will also want to use an external LED or do some other modifications. That's up to you :)
ampy -p /dev/ttyUSB3 put main.py
My parents have this Cuban internet connection using ADSL but it is too expensive to keep it on all the time and it has a captive portal you have to login to in order to have internet. I just wanted to have an indicator telling me when I can use the WiFi.