This commit adds the ability for x-pack extensions to optionally
provide custom roles providers, which are used to resolve any roles
into role descriptors that are not found in the reserved or native
realms. This feature enables the ability to define and provide roles
from other sources, without having to pre-define such roles in the security
config files.
relates elastic/x-pack-elasticsearch#77
Original commit: elastic/x-pack-elasticsearch@bbbe7a49bf
Dimitrios Athanasiou
Ali Beyad