When accessing private or institutional networks that require username/password in a login page, other browsers will automatically redirect you to a login page when they notice there is no internet access. I added an example below from Firefox which has an “Open Network Login Page” button, and a drop-down bar with the same button.
In the same system (Fedora 29) using Bave (Version 0.61.52 Chromium: 73.0.3683.86 (Official Build) (64-bit)) I only get a warning about HTTPS and not being able to load my desired page (much like the warning Firefox also gives), but no easy path to reach the network login page.
Could a similar button (or automatic redirection) be create in Brave?