Feature Request (API): Support Simple module for user authorization/management

[thantos]

Continuation from #247

There has been interest in Eventual coming packaged with simple opinionated user management. It should play well with the result of #247.

1. What are the primary features that should exist? Users, Attributes, Groups, Federation/Providers (facebook, google, LWA, etc).
2. Should it be based on Cognito or something 3P like Auth0?
3. ...

[yehudacohen]

Probably easiest for MVP is to support OIDC and maybe SAML integrations and just let people plug in their own identity providers.