It was already possible to sign in with Google+ or Facebook, it is now possible to join the platform with GitHub and LinkedIn!
You can thus link your CodinGame account to your GitHub or LinkedIn account (or both!) if you use the same email.
If you want to look at it, you have indeed to log out (hey this is one of the few times we'll tell you to log out from CodinGame) from your settings panel (yes it's kind of hidden)
We're thinking about integrating some cool stuff with GitHub and LinkedIn, so stay tuned for updates