Simplicity
A simple way to implement Facebook and Google login in your iOS apps
... app's binary, compared to 5.4MB when using the Facebook & Google SDKs. Simplicity is also extensible, and already supports other login providers, like VKontakte (the largest European social network) and generic OAuth providers. Simplicity is maintained by Stormpath, an API service for authentication, authorization, and user management. If you're building a backend API for your app, consider using Stormpath to help you implement a secure REST API.