Summary
We are providing the ability for enterprises to define custom roles with a set of fine-grained repo permissions that can be assigned to teams and users when adding them to repositories. This functionality provides Role-based access control (RBAC) support in GitHub Enterprise.

Intended Outcome
Greater flexibility and granularity for administering repo permissions through RBAC.

How will it work?
An organization administrator will be able to create custom roles, that inherit from our existing built-in roles, and customize a set of permissions for that role. Then, when a user or team is added to a repo the repo admin can then specify that role, which provides them a default set of permission grants.