@WRayX 

There is not a certified cert for local https access. The browser is showing that saying the data is not encrypted, but does not realize if you are connecting to a local device or remote. In your case you are only accessing the router from your computer, you do not go out to the internet, everything is local so connecting only via HTTP is fine.

If you were connecting to a banking site or credit card site, then that would be a major concern or accessing your router remotely.