This gets me 1 step further, the POST is indeed retried with WWW-Authenticate.
I also see the library checks the validity of my Kerberos ticket in the trace.

However i keep getting this error and even with running -vvv i get no more details. I have yet to browse the code for hints...

< HTTP/1.1 401 Unauthorized
< Content-Length: 1539
< Content-Type: text/html
< Server: Microsoft-IIS/6.0
* Authentication problem. Ignoring this.
< WWW-Authenticate: Negotiate YIGDBgkqhkiG9xIBAgIDAH50MHKgAwIBBaEDAgEepBEYDzIwMDUxMTAxMTIyNjAyWqUFAgMJH9imAwIBPKkMGwpGT0JPLkxPQ0FMqiYwJKADAgEDoR0wGxsEaG9zdBsTcG9jc3J2MDcuZm9iby5sb2NhbKwRBA8wDaEDAgEBogYEBGoAAMA=
< Date: Tue, 01 Nov 2005 12:26:02 GMT

Date: Mon, 31 Oct 2005 15:57:48 +0100 (CET)
From: Daniel Stenberg <daniel_at_haxx.se>
Subject: Re: IIS and Kerberos problem
To: the curl tool <curl-users_at_cool.haxx.se>
Message-ID: <Pine.LNX.4.63.0510311555200.11413_at_yvahk3.pbagnpgbe.fr>
Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed

On Mon, 31 Oct 2005, frank.vantol_at_bt.com wrote:

> Am i using the wrong commandline args ?
>
> curl http://pocsrv07/printers/hplj2200ps/.printer --data-binary @printpost
> -H User-Agent: -H Accept: -H Content-Type:" application/ipp" --trace -
> --negotiate

KNOWN_BUGS #10:

   To get HTTP Negotiate authentication to work fine, you need to provide a
   (fake) user name (this concerns both curl and the lib) because the code
   wrongly only considers authentication if there's a user name provided.
   http://curl.haxx.se/bug/view.cgi?id=1004841.

So you need to use something like "-u fake:fake" to trigger it.

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