With the current CEF implementation, it doesn't allow you to trigger window.open or even <a href="https://google.com" target="_blank">.
I understand that there may be Security Concerns by doing so however if it was possible to have something similar to electron ie the ability to include a package to execute loadExternalURL - which you then verify before trigging it to open.
The use cases for wanting this feature would be:
1) External Authentication Providers
2) Visiting Servers Websites ie Forums
3) Linking the account to Social Platforms
The issue for trying to provide them within the CEF would be: Username and Password management missing, No Cookies from existing Sessions therefore Authentication to any of these platforms would be a pain.
My example would be:
1) Join Server
2) Server attempts to detect if you have autheintcated with Discord in the past
3) If not offer a Login Button
4) opens External Page in default browser asking to authorize the application
5) Auth finished so returns to a Page that says return to RAGE
6) Rage has automatically processed the information