On Thu, 3 Apr 2008, CHADAL François [GIRCE] wrote:

> With the debug trace, I've seen the NTLM response send by the client (my
> application) is missing, often or always, when libcurl re-use another
> connection (number connection is different) to re-isssue the HTTP request.
> When it is OK, libcurl send the NTLM message header, and when libcurl switch
> for using another free connection, the NTLM message header is not present.
>
> It seems to be a bug.

This sounds exactly like this entry in docs/KNOWN_BUGS

37. Having more than one connection to the same host when doing NTLM
   authentication (with performs multiple "passes" and authenticates a
   connection rather than a HTTP request), and particularly when using the
   multi interface, there's a risk that libcurl will re-use a wrong connection
   when doing the different passes in the NTLM negotiation and thus fail to
   negotiate (in seemingly mysterious ways).

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