NTLM authentication using Windows.Web.Http.HttpClient

Question

I am working on a Windows 10 UWP app that needs to talk to a IIS server using NTLM authentication. I am setting the username and password in the HttpBaseProtocolFilter:

filter.ServerCredential = new PasswordCredential(uri, UserName, Password);

When i view the request in fiddler, it is using Basic Auth. Is there anything I can do to get it to use NTLM, which the server is requiring?

Request Headers:

Content-Length: 1459
Content-Type: text/xml; charset=utf-8
Host: server
Connection: Keep-Alive
Cache-Control: no-cache
Cookie: ClientId=XXXXXXXXX
Authorization: Basic XXXXXXXXX

Response Headers:

HTTP/1.1 401 Anonymous Request Disallowed
Server: Microsoft-IIS/8.5
request-id: xxxxx
WWW-Authenticate: NTLM
WWW-Authenticate: Negotiate
X-Powered-By: ASP.NET
X-FEServer: XXXXXXX
Date: Thu, 03 Dec 2015 16:12:58 GMT
Content-Length: 0
Proxy-Support: Session-Based-Authentication

Your code works for me with NTLM. Can you post the previous Fiddler requests and responses? — kiewic
– kiewic, Commented Dec 6, 2015 at 1:06
One note: I am setting the username for the password credential in the form: {domain}\{username} — Michael Sabin
– Michael Sabin, Commented Dec 7, 2015 at 15:49

Michael Sabin · Accepted Answer · 2015-12-10 03:28:48Z

Short answer: NTLM auth does work with username / password. Need to retry the connection a second time, because HttpClient is pre-sending BASIC auth when server wants NTLM

Long answer: My app contacts two services hosted on the same server. The first allows Basic auth but the second only allows NTLM. First I connected to the Basic auth service and then I connect to the NTLM one. I would assume the HttpClient would have automatically performed a retry with NTLM when it got the WWW-Authenticate: NTLM header, but it appears that it doesn't. However, if I manually retry the connection, then the second time the HttpClient will perform NTLM auth.

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