Question: What method can be used by a Network Function (NF) to forward a protected HTTP Request message towards a remote Public Land Mobile Network (PLMN) when communicating with a Security Edge Protection Proxy (SEPP)?
Option 1: Using a pre-shared secret key
Option 2: Utilizing the custom HTTP header "3gpp-Sbi-Target-apiRoot" in the HTTP request
Option 3: Including a digital signature in the HTTP request message
Option 4: Encrypting the HTTP request message with a symmetric key
Explanation: The correct answer is Option 2 because, according to the provided text, the custom HTTP header "3gpp-Sbi-Target-apiRoot" can be used by an NF within the SEPP's PLMN to forward the protected HTTP Request message towards a remote PLMN. This method allows for TLS protection between the SEPP and Network Functions or Service Communication Proxy (SCP) within a PLMN, as specified in clause 13.1.1.2 of the referenced document.