We did something similar to this at an org I worked at. We'd pull users from specific groups from our identity provider (Okta) and use that to provision corporate accounts to a Github Enterprise instance.

One big downside to this approach is Github teams often don't line up 1-to-1 with an organization's reporting structure, so you don't really ever get away from needing to manually manage user-team memberships, but it does remove the need to onboard/offboard users manually.