Nginx – How to use nginx to proxy to a host requiring NTLM authentication

It would be good to check IIS log files, to see if there's a pattern - are specific resources getting 401s or if it's generic.

A usual problem is certain resources could be in a server(file system) folder, and they may not be accessible to all users. These resources could be linked from specific pages alone, so the errors may be intermittent. Remember SharePoint runs requests in an impersonated context by default.

ntlm requires tcp sessions with keep alive enabled since it's bound to the tcp connection, it's usually off through a proxy or with short timeouts,and many proxies also use http 1.0 = one request per connection. ... which essentially gives the same problem. change authorization to kerberos, digest or plain auth. neither should be a problem if site is in ssl if you run in accelerated mode.

best option is if you can change your proxy software though, look for keep-alive and http 1.1 connections. have no experience of microsoft proxy server I'm from another camp, but I'm pretty sure that what you are experiencing is what I describe.

regards,

peter