>Check cache.log for any mentions of problems. Perhapse enable debugging >with -d on the helper to see if there is an issue with the validation. Thanks for the tip. Indeed, I've run squid with the -X flag and got a pretty clear error for that request, while everything's fine for the others : [...] 2011/08/10 18:22:54.040| authenticateNTLMHandleReply: helper: '0x1d3ccc08' sent us 'AF expinet.colissimo' 2011/08/10 18:22:54.040| authenticateNTLMHandleReply: Successfully validated user via NTLM. Username 'expinet.colissimo' 2011/08/10 18:22:54.845| authenticateNTLMHandleReply: helper: '0x1d3ccc08' sent us 'TT TlRMTVNTUAACAAAADAAMADAAAAAFgomiVcvIuzNYgBwAAAAAAAAAAHYAdgA8AAAAUABJAEMASABPAE4AAgAMAFAASQBDAEgATwBOAAEAEgBGAFcALQBNAEEAUwBUAEUAUgAEABgAcABpAGMAaABvAG4ALgBsAG8AYwBhAGwAAwAsAGYAdwAtAG0AYQBzAHQAZQByAC4AcABpAGMAaABvAG4ALgBsAG8AYwBhAGwAAAAAAA==' 2011/08/10 18:22:54.845| authenticateNTLMHandleReply: Need to challenge the client with a server blob 'TlRMTVNTUAACAAAADAAMADAAAAAFgomiVcvIuzNYgBwAAAAAAAAAAHYAdgA8AAAAUABJAEMASABPAE4AAgAMAFAASQBDAEgATwBOAAEAEgBGAFcALQBNAEEAUwBUAEUAUgAEABgAcABpAGMAaABvAG4ALgBsAG8AYwBhAGwAAwAsAGYAdwAtAG0AYQBzAHQAZQByAC4AcABpAGMAaABvAG4ALgBsAG8AYwBhAGwAAAAAAA==' 2011/08/10 18:22:54.854| authenticateNTLMHandleReply: helper: '0x1d3ccc08' sent us 'AF expinet.colissimo' 2011/08/10 18:22:54.855| authenticateNTLMHandleReply: Successfully validated user via NTLM. Username 'expinet.colissimo' 2011/08/10 18:22:57.166| authenticateNTLMHandleReply: helper: '0x1d3ccc08' sent us 'TT TlRMTVNTUAACAAAADAAMADAAAAAFgomiBYi9jX1PfFAAAAAAAAAAAHYAdgA8AAAAUABJAEMASABPAE4AAgAMAFAASQBDAEgATwBOAAEAEgBGAFcALQBNAEEAUwBUAEUAUgAEABgAcABpAGMAaABvAG4ALgBsAG8AYwBhAGwAAwAsAGYAdwAtAG0AYQBzAHQAZQByAC4AcABpAGMAaABvAG4ALgBsAG8AYwBhAGwAAAAAAA==' 2011/08/10 18:22:57.166| authenticateNTLMHandleReply: Need to challenge the client with a server blob 'TlRMTVNTUAACAAAADAAMADAAAAAFgomiBYi9jX1PfFAAAAAAAAAAAHYAdgA8AAAAUABJAEMASABPAE4AAgAMAFAASQBDAEgATwBOAAEAEgBGAFcALQBNAEEAUwBUAEUAUgAEABgAcABpAGMAaABvAG4ALgBsAG8AYwBhAGwAAwAsAGYAdwAtAG0AYQBzAHQAZQByAC4AcABpAGMAaABvAG4ALgBsAG8AYwBhAGwAAAAAAA==' 2011/08/10 18:22:57.176| authenticateNTLMHandleReply: helper: '0x1d3ccc08' sent us 'AF expinet.colissimo' 2011/08/10 18:22:57.176| authenticateNTLMHandleReply: Successfully validated user via NTLM. Username 'expinet.colissimo' 2011/08/10 18:22:58.629| authenticateNTLMHandleReply: helper: '0x1d3ccc08' sent us 'TT TlRMTVNTUAACAAAADAAMADAAAAAFgomi/vpkDjFtgzcAAAAAAAAAAHYAdgA8AAAAUABJAEMASABPAE4AAgAMAFAASQBDAEgATwBOAAEAEgBGAFcALQBNAEEAUwBUAEUAUgAEABgAcABpAGMAaABvAG4ALgBsAG8AYwBhAGwAAwAsAGYAdwAtAG0AYQBzAHQAZQByAC4AcABpAGMAaABvAG4ALgBsAG8AYwBhAGwAAAAAAA==' 2011/08/10 18:22:58.629| authenticateNTLMHandleReply: Need to challenge the client with a server blob 'TlRMTVNTUAACAAAADAAMADAAAAAFgomi/vpkDjFtgzcAAAAAAAAAAHYAdgA8AAAAUABJAEMASABPAE4AAgAMAFAASQBDAEgATwBOAAEAEgBGAFcALQBNAEEAUwBUAEUAUgAEABgAcABpAGMAaABvAG4ALgBsAG8AYwBhAGwAAwAsAGYAdwAtAG0AYQBzAHQAZQByAC4AcABpAGMAaABvAG4ALgBsAG8AYwBhAGwAAAAAAA==' 2011/08/10 18:22:58.639| authenticateNTLMHandleReply: helper: '0x1d3ccc08' sent us 'NA NT_STATUS_NO_SUCH_USER' 2011/08/10 18:22:58.639| authenticateNTLMHandleReply: Failed validating user via NTLM. Error returned 'NT_STATUS_NO_SUCH_USER' The challenge might be wrongly generated by the client, though it'd be weird given the previous ones are correct. Or, if it's still related to the POST data length being zero, just to clear things up, do you know if it's (the POST data) used by the challenge generation algorithm? >What application is this? there are two bugs in those headers that need >reporting. Not related to your NTLM problems though. It's a Windows software, I don't know which client HTTP library is used.
