When plasma-nm connects to a network and detects that there is no Internet access, it emits a notification to the effect that the user needs to log in to the network.

Rather than simply informing the user of the need to log in, please add a configuration option (either global or for each network) that, when enabled, will also cause plasma-nm to automatically open the system default web browser to http://networkcheck.kde.org/, without the user needing to click on anything first.  This will save some time, especially for users that very frequently connect to networks requiring such logins.