; SIP example:
; WWW‑Authenticate: Digest realm="atlanta.
; nonce="84f1c1ae6c
; opaque="", stale=FALSE, algorithm=MD5
; IMS example:
; SIP/2.0 401 Unauthorized
; ...
; WWW-Authenticate: Digest realm="registrar.home1.net",
; nonce=base64(RAND + AUTN + server specific data),
; algorithm=AKAv1‑MD5,
; ik="0011223344
; ck="ffeeddccbb
; CSeq: 1 REGISTER