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Use an Identity Provider (IDP)*. Other people have mentioned LDAP, which can play this role.
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Use groups within the IDP to declare who has what privileges.
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Apps using the IDP for auth can read the groups and allow/deny permissions based on groups.
*Or Identity and Access Management if you are in the cloud ig.
For open source solutions, I would recommend:
- Authentik (what I use)
- Kanidm (doesn't have web ui)
- Nubus by Univention
These three solutions all have invites, ldap, and can act as oauth providers. (Oauth is single sign on), which are the features I want. There are also integrated, including it all in the one app.
There is also LLDAP, which is a web ui for ldap, and then you could use a service that connects to that, like authelia or keycloak, to add oauth on top.

Second comment, but also check out midpoint by evoloum: https://docs.evolveum.com/iam/
It is a modern web frontend on top of Active Directory.