Captive portal login page does not automatically open on some WiFi networks

Description

On WiFi networks that require web-based authentication (captive portals), Linux Mint does not automatically detect the captive portal or open the login page.

The system connects to the WiFi network successfully, but the browser redirect/login page does not appear, and no notification or button is provided to open it.

In my case, I was eventually able to find the URL that the WiFi network wanted to redirect me to after a colleague of mine, who was using Windows, accessed the captive portal and I was able to get the link from there. I signed in on the website and the network worked like any normal network.

I searched for about half an hour to report this to the correct upstream repository and found that the issue is most likely related to NetworkManager:

https://gitlab.freedesktop.org/NetworkManager/NetworkManager

However, GitLab is currently not accepting new account signups, so I am reporting it here instead.

Could you please confirm whether this is the correct component and repository for this issue? If it belongs upstream, I would appreciate it if you could point me to the appropriate place or forward the report if possible.

I am happy to provide any additional information, or answer any questions that may help investigate the issue.

Environment

Linux Mint: 22.3 Cinnamon

Cinnamon: 6.6.7

NetworkManager: 1.46.0-1ubuntu2.7

Start by confirming whether captive-portal detection belongs to Cinnamon or NetworkManager, using the reported Linux Mint, Cinnamon, and NetworkManager versions and the linked upstream repository. Done means identifying the correct component and producing or forwarding a reproducible report with the relevant network details.