[Devel] authorizing based on p-preferred-identity

[Juha Heinanen]

some sip UAs add rfc3325 p-preferred-identity header into requests that
contain the identity the UA wishes to use instead of the one in from
header.  this is especially useful when from header is anonymous.

radius_proxy_authorize and maybe also other similar functions use from
header to obtain realm (unless realm is given as parameter to the
function) and user to be authorized.  

i suggest that radius_proxy_authorize takes two pseudo variables as
arguments that specify user and realm.  that way, they can be taken
either from from header or from p-preferred-identity header, or
somewhere else.

is it ok that i implement such a change and also add pseudo variables
for obtaining ppi header user and host (for sip or sips uri only)?

-- juha