Sitecore 9 Federated Authentication
This sample code enables visitors to log it to the site using Facebook and Google. Also enables editors to log in to sitecore using OKTA.
See post for full details. http://josedbaez.com/2018/03/sitecore9-sso/
Note: This might have references to newer dlls (e.g. newtonsoft and owin). Make sure you update your site binding redirects or downgrade to sitecore's default and test.