[Serusers] 401 vs. 407 challenge

[Greg Fausak]

In debugging yet another SIP hardware device I
found that it was not authenticating after an
INVITE.  That is, the device sends me 'INVITE', I say
'401', it says 'ACK', but I never hear from it again.

I am expecting another INVITE with the proper credentials...

In talking with the hardware vendor they let me know that
I should be sending back a 407 instead of a 401.
I have always done a www_challenge sequence, but,
I wonder if that is truly proper.  After all, SER is
a proxy.  Should I be challenging with a 'proxy_challenge'?

Certainly either should work, because the device you
are communicating with could be a UA or a PROXY.
What is the 'proper' thing to do?

I guess I have always thought that the 'proxy_challenge'
was for one proxy server communicating with another.
However I don't see how that can be now, because the
originating proxy server has no mechanism to provide
authentication credentials...

The more I learn, the less I know,

---greg