If you use Facebook or Twitter, anyone who already has a presence there can access your app. Given the popularity of these platforms, this can be an easy way to allow your users access.

If you choose GitHub, then your user base should be heavily oriented toward developers. Not every developer has a GitHub account, but a large number do. This can be a boon for apps that are tilted in this direction.

If you choose Google, another vast collection of users will be available to you.

If you choose Okta, a commercial system you can configure and use, then you have 100% control. Your users don’t have to exist on any social media platform and they don’t have to be developer oriented. You have complete control while still being able to outsource the hard parts of user management.