Comment 4 for bug 1571522

connman does a really good job here in implementing WiSPr (https://en.wikipedia.org/wiki/WISPr) support to deal with captive portals.

If you want to check if you're really not on an captive portral you want to implement something like this to perform a check if you're "online" or not:

1. Setup a well known server, lets say online.ubuntu.com which returns respecific HTTP headers like X-Ubuntu-Online: true once a HTTP GET request is received
2. When NetworkManager performs a check if its online or not (when connected to a new WiFi network or when the IP configuration has changed) it can send a HTTP GET request to online.ubuntu.com and if it gets the X-Ubuntu-Online header back its really online and otherwise not.

There is not right way to rely on result codes as those are not reliable. The one way is to set up an endpoint which will return a set expectation if you're really online.

This feature would be really something to add to NetworkManager rather than indicator-network.