Thanks to some great guides on the Internet I was able to configure a Squid 3.1.19 installation (Ubuntu 12.04 x64) to do a SingleSignOn with our Active Directory User accounts: if a domain users starts his/her browser, the proxy does not require credentials, as it is fetching them automatically. The problem is now that sometimes, after some time of browsing and (so it seems) with no order at all the browser shows a login popup. If I check the access.log I see a lot of entries, some with no user (as normal with NTLM, it needs another request), but I'm not able to find the cause of the popup. Here are some lines from the access.log: And here's the (relevant) part of the squid.conf: Thanks you for any input that maybe could solve my problem. ;) -- View this message in context: http://squid-web-proxy-cache.1019090.n4.nabble.com/SingleSignOn-NTLM-Still-showing-login-popups-sometimes-tp4662690.html Sent from the Squid - Users mailing list archive at Nabble.com.