FreeIPA 3.x is a very powerful replacement for MS AD. As it turns out, it also contains a full RBAC system that has host-based differentiation capabilities.

Imagine: Individual permissions allow very granular mapping to actual functions in the Atlassian stack. Traditional Atlassian roles such as jira-administrator allow a smooth migration path for existing users. Privileges are created to map these permissions to roles. Add hosts to the mix, and roles can be differentiated by server such that the jira-administrator role can be the same everywhere, but with only certain users available to exercise a role per host.

FreeIPA does all this out of the box.

Crowd is great, but FreeIPA has slowly improved to where Crowd was originally going to go. FreeIPA is incredibly detailed, maybe too detailed for the beginner user. As it's turned out, they compliment each other quite remarkably! Supporting both Crowd and FreeIPA will make the Atlassian stack incredibly valuable.