ASP MVC Preview 5 and IIS 6 Windows Authentication

Question

I've just built a basic ASP MVC web site for deployment on our intranet. It expects users to be on the same domain as the IIS box and if you're not an authenticated Windows User, you should not get access.

I've just deployed this to IIS6 running on Server 2003 R2 SP2. The web app is configured with it's own pool with it's own pool user account. The IIS Directory Security options for the web app are set to "Windows Integrated Security" only and the web.config file has:

<authentication mode="Windows" />

From a Remote Desktop session on the IIS6 server itself, an IE7 browser window can successfully authenticate and navigate the web app if accessed via http://localhost/myapp.

However, also from the server, if accessed via the server's name (ie http://myserver/myapp) then IE7 presents a credentials dialog which after three attempts entering the correct credentials eventually returns "HTTP Error 401.1 - Unauthorized: Access is denied due to invalid credentials".

The same problem occurs when a workstation browses to the web app url (naturally using the server's name and not "localhost").

The IIS6 server is a member of the only domain we have and has no firewall enabled.

Is there something I have failed to configure correctly for this to work?

Thanks,

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I have tried the suggestions from Matt Ryan, Graphain, and Mike Dimmick to date without success. I have just built a virtual machine test lab with a Server 2003 DC and a separate server 2003 IIS6 server and I am able to replicate the problem.

I am seeing an entry in the IIS6 server's System Event Log the first time I try to access the site via the non-localhost url (ie http://iis/myapp). FQDN urls fail too.

Source: Kerberos, Event ID: 4
The kerberos client received a KRB_AP_ERR_MODIFIED error from the server host/iis.test.local. The target name used was HTTP/iis.test.local. This indicates that the password used to encrypt the kerberos service ticket is different than that on the target server. Commonly, this is due to identically named machine accounts in the target realm (TEST.LOCAL), and the client realm.

Answer 1

It sounds to me as though you've done everything right.

I'm sure you are but have you made sure you are using 'DOMAIN\user' as the user account and not just 'user'?

Answer 2

Sounds like the new Loopback check security feature of Windows Server 2003 SP1. As I understand it, is designed to prevent a particular type of interception attack.

From http://support.microsoft.com/kb/896861

SYMPTOMS

When you use the fully qualified domain name (FQDN) or a custom host header to browse a local Web site that is hosted on a computer that is running Microsoft Internet Information Services (IIS) 5.1 or IIS 6, you may receive an error message that resembles the following: HTTP 401.1 - Unauthorized: Logon Failed This issue occurs when the Web site uses Integrated Authentication and has a name that is mapped to the local loopback address.

Note You only receive this error message if you try to browse the Web site directly on the server. If you browse the Web site from a client computer, the Web site works as expected.

CAUSE

This issue occurs if you install Microsoft Windows XP Service Pack 2 (SP2) or Microsoft Windows Server 2003 Service Pack 1 (SP1). Windows XP SP2 and Windows Server 2003 SP1 include a loopback check security feature that is designed to help prevent reflection attacks on your computer. Therefore, authentication fails if the FQDN or the custom host header that you use does not match the local computer name.

Workaround

• Method 1: Disable the loopback check
• Method 2: Specify host names

See http://support.microsoft.com/kb/896861 for details.

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Edit - just noticed that you said you were seeing this from Client PCs as well... that's more unusual. But I'd still look to test one of these workarounds, to see if it corrected the problem (and if so, might indicate a problem with your DNS config).

Answer 3

IE7 only sends Windows credentials (NTLM, Kerberos) if it identifies the server as being on the Intranet. IE7 also added an Intranet zone lockdown feature - if you're not on a domain, by default no servers are in the Intranet zone. This was done to prevent zone-migration attacks.

To change this, go to Tools/Internet Options, Security tab, then click Local Intranet. You can then manually add servers that should be treated as Intranet, by clicking the Sites button, then Advanced, or tell IE not to automatically detect your Intranet and selecting the other checkboxes as appropriate.

Answer 4

I just encountered the opposite problem - my site authenticates externally but not locally.

I compared it to the sites we have working and the difference was that the site that failed to authenticate was using Windows Authentication.

However, other sites I work with (this is a dev server) tend to have Basic Authentication.

Not sure why exactly but this fixed it.

However, at the same time I noticed "Default Domain" and "Realm" settings.

I know it's very unlikely but could these perhaps help at all?

Answer 5

After extensive Googling I managed to find a solution on the following MSDN article:
How To: Create a Service Account for an ASP.NET 2.0 Application

Specifically the Additional Considerations section which describes "Creating Service Principal Names (SPNs) for Domain Accounts" using the setspn tool from the Windows Support Tools:

setspn -A HTTP/myserver MYDOMAIN\MyPoolUser
setspn -A HTTP/myserver.fqdn.com MYDOMAIN\MyPoolUser

This solved my problem on both my virtual test lab and my original problem server.

There is also an important note in the article that using Windows Authentication with custom pool users constrains the associated DNS name to be used by that pool only. That is, another pool with another identity would need to be associated with a different DNS name.