Even when we set bnconfig to https://forums.abc.com it is not adding redirect url https://forums.abc.com/ instead it is making http://https// (Please notice no colon( : ) after https) which is totally wrong. By the way if we are skipping the protocol in bnconfig command it is making http redirect url to http which is not secure.
Is your discourse site behind a proxy? If so, you will need to set the x-forwarded-proto header. This topic has more information on configuring a reverse proxy: