P-CSCF1 removes any keys received in the 401 Unauthorized response and forwards the rest of the
response to UE1.
WWW-Authenticate:
P-CSCF1 removes the ik and ck parameters (directives) from the header.
Security-Server:
q is the preference value, 0.1 means IPsec is the first preferred choice. The q value
represents only relative degradation of all mechanisms listed here. The lower value, the
higher prority.