3GPP 23.501 v20.2.0 — the document's own text
5.2.4 Authorisation
Taught in 7. Every name the system uses (The 5G system architecture, in depth), 18. Being served by somebody else's network (The 5G system architecture, in depth), 4. Knowing who you are and where you are (The 5G system architecture, overview).
The authorisation for connectivity of the subscriber to the 5GC and the authorization for the services that the user is allowed to access based on subscription (e.g. Operator Determined Barring, Roaming restrictions, Access Type and RAT Type currently in use) is evaluated once the user is successfully identified and authenticated. This authorization is executed during UE Registration procedure.