What? You can use Cognito User Pools to sign-up and manage user accounts in-house. That's the core of any identity solution. You can hook up Google, Facebook, etc. as identity providers if you want to give your users a third-party sign-in option.
Maybe I'm misunderstanding your use case, so correct me if I got something wrong.
Maybe I'm misunderstanding your use case, so correct me if I got something wrong.