Certain IPC requests to the attribute manager, CIB manager, and controller have an `acl_target` XML attribute with the ACL user name. Before 1.1.12, this was `attr_user` for the attribute manager, `cib_user` for the CIB manager, and `crm_user` or `lrmd_ipc_user` for the controller. `pcmk__update_acl_user()` sets both the current and legacy attributes for compatibility in rolling upgrads. Once we drop support for rolling upgrades and remote client connections from earlier versions (see the subtasks), we can stop adding the legacy attributes.
Also before 1.1.12, the CIB had different syntax for ACLs. These were changed at the time in the schema via transforms, but the CIB manager doesn't upgrade CIB schemas, so it had to support the old syntax during rolling upgrades. This support and related cts-cli tests have already been dropped for 3.0.0 via [[https://github.com/ClusterLabs/pacemaker/pull/3508 | CLPR#3508]].