This feature is _incorrectly_ named, its supposed to be Membership-
With so many SaaS apps, adoption of ASP is so far behind, primarily leaving out membership components for groups/tenants (with the turn of a switch/configurable).

Many will argue its not membership, however - a group/company similar to users, i.e. it also has access/features/roles/components enabled at the group level for e.g. free/pro/premium or non-profits/commercial etc.
IMHO it is a subset of membership. This has not been properly addressed and been punted for a very long time. Further - this is an aspect/AOA of the systems authorization and security, that's commons to many SaaS apps/developers, impeding the rolls out of SaaS apps. Many are reinventing the wheel.
I really like johns sample on ASP MVC group management
As we've said, ASP.NET identity is not aimed at multi-tenancy. It's identity, because that's what it is, it provides a database schema and support for logging in with either a local or federated identity. There's nothing to stop you adding your own groups support, it is, after all, just a bunch of EF models.