Question: What triggers the secondary authentication procedure with a DN-AAA server after successful primary authentication?
Option 1: The establishment of the Onboarding PDU Session and the use of non-default UE credentials.
Option 2: The failure of primary authentication as described in I.9.2.2 or I.9.2.3.
Option 3: The ON-SNPN, upon the establishment of the Onboarding PDU Session, using Default UE credentials for secondary authentication.
Option 4: The DN-AAA server, after receiving a request from the UE.
Explanation: Secondary authentication is triggered by the ON-SNPN when it establishes an Onboarding PDU Session and uses default UE credentials for secondary authentication. This ensures that the UE's identity is further verified before granting access to network resources.