I've written an implementation of Geni OAuth2 using the PHP library HybridAuth for anyone who wants to build it out. I've also implemented it for MyHeritage and FamilySearch. You can see a demo here as well as find the link to the GitHub.
Nothing on that site is stored in a database, so you can authenticate without worry. If anyone wants to help we could extend the entire Geni API to work within the library. Let me know if anyone wants to help.