support for backend for multi-tenants

[daniel-garcia]

Swagger petstore.jwt.swagger:

      properties:
...
        # tenant_ref is a non-standard claim
        tenant_ref:
          type: string
          example: "SD_ZOO"
          description: "tenant_ref claim provides the tenant reference for a petstore.  equivalent uses: account_id, org_id, ..."

SEAL context rule:

context {
    where subject.tenant_ref == "SD_ZOO";
} ... {
...
}

[wplu]

The above commit defines the field in the JWT to illustrate the use of multi tenants. That jwt field tenant_ref should be used in the implementation demo.