Playground doesn't ask for seperate credentials, instead it allows login via popular identity providers so that users don't need to remember other set of credentials. Users can signup/login anytime with any of supported providers and they should be up & running very quickly.
Login specifically matches user's email address within Playground and allows to login even if you are using different identity provider second time, thus making the whole process really simple.
- Signup/Login methods matches with email address.
- Any provider can be used to login into account until & unless email address is same.
- Users will not have access of this app if for some reason, they don't own original email address with which they logged in.