Add a Post-Login Action for adding MinIO-friendly policy claims

[mblomdahl]

Checklist

• I have looked into the Readme, and Contributing guide and have not found a suitable solution or answer.
• I have searched the issues and have not found a suitable solution or answer.
• I have searched the Auth0 Community forums and have not found a suitable solution or answer.
• I agree to the terms within the Auth0 Code of Conduct.

Describe the problem you'd like to have solved

I want my users to be able to login to MinIO Console with social connection and get the appropriate permissions' policy attached to their user profiles.

Describe the ideal solution

I would like my Auth0 tenant to apply some logic that allows me to map users to policies in MinIO and propagate this authorization to the MinIO application. I would also like to have a default low-privilege policy assignment for random strangers.

Alternatives and current workarounds

I can use the current role-creation-POST_LOGIN template to assign the same role to all known users. The downside of this is ...

1. I would also like to have a OpenID integration with Kubernetes (I want to be able to authenticate with Kubernetes as me, via OpenID/SSO OwnTube-tv/minio-microk8s-ansible#12) and having this "one special group" and no JWT Claim prefix/namespacing makes it hard to use side-by-side with MinIO JWT Claims
2. I'd like to add different special users to different policies, not all should be granted the same (me, for example, I want to be an admin, but my friends should only have read-write permissions)
3. There is no graceful way to make unknown users/bots/strangers be allowed to login to a fallback read-only role

Additional context

I'm trying to complete this ticket, OwnTube-tv/minio-microk8s-ansible#10