Add checksession endpoint to OpenIddict ASOS

I would like to add the checksession endpoint to OpenIddict, it seems that there is a way to do that: https://kevinchalet.com/2016/07/13/creating-your-own-openid-connect-server-with-asos-introduction/ But there is not information how to add the checksession endpoint configuration to OpenIddict also the same issue for the back chanel logout Any body konw if this is possible? Best regards