Here is how you set up the GITHUB_CLIENT_ID and GITHUB_CLIENT_SECRET credentials that you need when using Github as an OAuth provider.

Navigate to the Developer Settings, OAuth Applications

To get there:

Step What it looks like
1. Choose Settings from upper right drop down menu next to your personal avatar choose settings menu
2. Find the Developer Menu, which is pretty far down the page on the left hand side. Find OAuth Applications on that menu choose OAUTH applications from developer menu

The page that shows the callback url

The page with the GITHUB_CLIENT_ID and GITHUB_CLIENT_SECRET