Unable to Access the MS Sharepoint using Squid 3

Resolution

There is no solution for this for Squid-3.1. The community developers state that is not necessary to perform a backport patches for these authentication problems found in Squid-3.1 because these issues was already solved in Squid-3.2.

There are many complex changes that have to be made in the Red Hat shipped version of Squid-3.1 and because of that, this kind of fixes can not be considered as a backport, and as the same of community version, these issues will be fixed only in Squid-3.2 that will be shipped in RHEL7.

Possible Workarounds

A workaround can be to use the community version of Squid-3.2. Such an installation will only be giving up Red Hat support with regard to this package in particular, but the system will continue to be supported normally. For any questions or problems where a Squid is not involved, Red Hat will usually assist.

Another possibility in case of Windows clients (i.e. browsers) may be to implement a workaround with a proxy autoconfiguration file (Windows Proxy Auto Discovery, WPAD). It should be setup that all the clients connect directly to the problematic Sharepoint server instead of going through the proxy. Please, see the following code snippet that implements this functionality:

function FindProxyForURL(url, host)
{
        // NLTM authentication to MS SharePoint is broken in Squid 3.1.10
        // so always use direct connection to SharePoint server
        if ( dnsDomainIs(host, "www.sharepointserver.com"))
        {
                return "DIRECT";
        }

        // Otherwise use Squid proxy (with fallback to direct connection if proxy server is unavailable)
        return "PROXY squidproxy.com:3128; DIRECT";
}