Question: What is a primary security mechanism that the Common API Framework (CAPIF) must provide for interactions between itself and external API invokers, as per 3GPP security requirements?
Option 1: Mutual Authentication between CAPIF and API Invoker, ensuring both parties verify each other's identity.
Option 2: Encryption of API responses only, to protect sensitive information.
Option 3: Authorization based solely on the API invoker's IP address.
Option 4: Validation of API requests through a third-party service.
Explanation: Mutual Authentication is crucial for ensuring that both the CAPIF and the external API invoker are assured of each other's identities, preventing unauthorized access and man-in-the-middle attacks, thereby protecting the Public Land Mobile Network (PLMN) trust domain from external threats.