Captive portal detection may not be working

Edward reported having problems logging into an airplane’s captive portal on Slack: https://bravesoftware.slack.com/archives/C2FQMN4AD/p1582408566001200

Chrome and Firefox both have code to detect these portals and are using these test endpoints:

• http://clients3.google.com/generate_204
• http://detectportal.firefox.com/canonical.html

Testing is going to be challenging, but I found a potentially-useful node app on the Firefox meta-bug and there is a BadSSL test page for Chrome which triggers the UI in Brave too.

[antonok-edm]

If anyone urgently needs to connect to the internet in the meantime, and is willing to make the tradeoff of using Google’s generate_204 endpoint, this should suffice as a workaround:

1. Make sure Brave is not currently running
2. Find your browser’s profile directory, e.g. ~/.config/BraveSoftware/Brave-Browser/ on Linux
3. Find your profile’s Preferences file within the profile directory, e.g. ./Default/Preferences
4. Modify it such that the alternate_error_pages.enabled key is present and set to true, e.g.:

{"alternate_error_pages":{"backup":false,"enabled":true},...

1. Start Brave and connect to the captive portal
2. (optional) Close Brave and modify the file again to remove the key-value pair added in step 3

[wknapik]

I’m using a network now where Firefox and Chromium on Linux have no issue detecting the captive portal and show me an option to go through it, but Brave doesn’t appear to be aware of it at all and attempts to visit any website simply fail.

For people who travel a lot, that seems like a must-have feature.

cc @rebron