Section: 13.3.2.2 Indirect communication
Content: In indirect communication scenarios, the NF Service Producer and NF Service Consumer shall use implicit authentication by relying on authentication between NF Service Consumer and SCP, and between SCP and NF Service Producer, provided by the transport layer protection solution, NDS/IP, or physical security. NOTE 0: Mutual authentication between NF Service Consumer and NF Service Producer is not achieved with hop-by-hop security. If the PLMN uses token-based authorization as specified by clause 13.4.1.2 and the PLMN’s policy mandates that the NRF authenticates the NF Service Consumer before granting an access token, the access token indicates to the NF Service Producer that the NF Service Consumer has been authenticated by the NRF. If additional authentication of the NF Service Consumer is required, the NF Service Producer authenticates the NF Service Consumer at the application layer using CCA based authentication as specified in clause 13.3.8. The NF Service Consumer authentication based on CCA based authentication is optional to use, and based on operator policy.