General expected data model:

( tenants >--< users ) --< roles

Tenants and Users have a many-to-many relationship. A given Tenant-User pair can have many Roles.

Tenant Schema:

id: something big and unique name: something displayable .. created_at: datetime .. deleted_at: datetime

User Schema:

id: something big and unique name: something displayable .. created_at: datetime .. deleted_at: datetime

General service model:

1. a web service with an API
2. a variety of backend storage schemes for tenant-user pairs.
3. a simple token datastore