Office Communicator 2007 R2 doesn't authenticate with proxy when connecting to outbound server

Question

I am trying to connect to OCS 2007R2 from behind an authenticated proxy. The proxy doesn't block addresses or ports, but uses a domain authentification, for which I have credentials with which I am currently logged into Windows.

The client is configured to connect to the Microsoft OC server pool1.oconline.microsoftonline.com:443 with TLS, and this configuration works from my home.

The client is the standard one running on W7x86, and the log for the failed attempt contains this:

02/09/2011|14:48:38.136 1B8C:BAC INFO  :: ASYNC_SOCKET::SetHttpProxyAddr HttpProxyAddr [172.31.XXX.XXX:8080]
02/09/2011|14:48:38.136 1B8C:BAC INFO  :: ASYNC_SOCKET::Connect - Tunneling [yes] - DestAddr [65.55.50.39:443] - Host [pool1.oconline.microsoftonline.com:443] - RemotePrincipalName - [pool1.oconline.microsoftonline.com], this 04CD1FC0
02/09/2011|14:48:38.151 1B8C:1A04 TRACE :: Entering callback SIP_MSG_PROCESSOR::HttpProxyCallback 64
02/09/2011|14:48:38.151 1B8C:BAC TRACE :: ASYNC_SOCKET::SendHttpConnect send request: CONNECT pool1.oconline.microsoftonline.com:443 HTTP/1.0

Host: pool1.oconline.microsoftonline.com

Proxy-Connection: Keep-Alive

Pragma: no-cache



 size 149
02/09/2011|14:48:38.151 1B8C:BAC TRACE :: ASYNC_SOCKET::SendOrQueueIfSendIsBlocking sending sendBuffer 04D05688, this FEDCBA98, pSendBuffer->m_BufLen = 149
02/09/2011|14:48:38.151 1B8C:BAC TRACE :: ASYNC_SOCKET::SendHelperFn sendBuffer 04D05688 sent, this 04CD1FC0, m_BytesSent = 149, pSendBuffer->m_BufLen = 149
02/09/2011|14:48:38.151 1B8C:1A04 TRACE :: Entering callback SIP_MSG_PROCESSOR::HttpProxyCallback 32
02/09/2011|14:48:38.151 1B8C:1A04 TRACE :: Entering callback SIP_MSG_PROCESSOR::HttpProxyCallback 33
02/09/2011|14:48:38.151 1B8C:1A04 TRACE :: Entering callback SIP_MSG_PROCESSOR::HttpProxyCallback 46
02/09/2011|14:48:38.151 1B8C:1A04 TRACE :: Entering callback SIP_MSG_PROCESSOR::HttpProxyCallback 46
02/09/2011|14:48:38.182 1B8C:BAC ERROR :: ASYNC_SOCKET::GetProxyResponse cannot connect to http proxy, status 407
02/09/2011|14:48:38.182 1B8C:BAC ERROR :: ASYNC_SOCKET::OnRecvComplete get proxy response failed error 80ee001c

The 407 error suggests that the client cannot authenticate with the proxy, thus preventing it to tunnel the SSL connection needed for the SIP protocol OCS uses.

I have had a similar 407 error with Microsoft Online Services, which I resolved using this article from Microsoft. As I can read the issue and the solution, it seems that somehow my computer connects to *.microsoftonline.com using the proxy, but somehow fails to authenticate with it.

I have had no problem connecting to internet with IE or Firefox, so I looked into the Internet Options from the Control Panel. I have the following:

• No automatic settings detection.
• No automatic configuration script.
• Use a proxy server, same for all protocols.
• Bypass proxy server for local address.
• Exceptions do not use proxy server:10.250.*;192.168.3.*;172.31.5.*;192.168.254.*

Also, in the Security Settings tab of the Internet Options, https://*.microsoftonline.com is in the Local intranet. It doesn't mean it doesn't use the proxy to connect, it just means it uses Medium-Low security settings (which include automatic domain authentication to local addresses). I didn't choose this, it seems that Microsoft Online Services sets it like this.

So my best shot would be to find an equivalent of the trick I used to connect Online Services. Or maybe write my own .pac automatic configuration script. Has anyone seen something like this before?