OmniAuth strategy for Kongregate authentication

Current version is mostly focused on auto-detecting the logged-in user when the application is running on a canvas.

Just add the provider as usual, passing your app's Kongregate API key (add /api to the URL to get it). For example:

Rails.application.config.middleware.use OmniAuth::Builder do
  provider :kongregate, 'YOUR_API_KEY'
end

When your game is first open on Kongregate, redirect to /auth/kongregate (preserving the kongregate_user_id and kongregate_game_auth_token parameters) to perform the authentication.

If the token is valid, /auth/kongregate/callback will fire. You can get the validated user_id and the username there with:

auth = request.env['omniauth.auth']
user_id = auth.uid
username = auth.extras['username']

Guest access (users that are not logged in on Kongregate) will result in an auto-generated, non-numeric value in user_id (so it won't clash with kongregate_user_id), prefixed with "g_", so applications have a set of temporary credentials until the user decides to authenticate.

• Display the Kongregate login form for non-authenticated users

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Added some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request

• pmariano, for implementing guest access.