unknown unknown - 2 months ago 20
ASP.NET (C#) Question

why does windows authentication / impersonation fail on asp.net application with iis 7.5 / windows 7 /

I'm troubleshooting why I can't get past the login dialog on an ASP.Net site configured for Windows Authentication and Impersonation.

I have an ASP.Net 2.0 application and I'm trying to deploy it on Windows 7 with IIS 7.5. I've created a new site, and bound it to localhost and a fully qualified domain name. the FQDN is in my hosts file, and is redirected to

The site is also running with an AppDomain I created, with integrated pipeline mode, and the process model identity is set to ApplicationPoolIdentity.

Web.config includes the following:

<trust level="High" />
<authentication mode="Windows" />
<deny users="?"/>
<identity impersonate="true"/>`

ACL on the directory for the site is set to Everyone (Full Control - For testing).
The Application Pool virtual account (Windows 7 thing) is set to full control on the physical directory for the site also.

IIS authentication has ASP.Net impersonation enabled and Windows Authentication enabled.

When I connect to the site as localhost, it permits me to get past the login prompt and the application loads without incident.

When I connect to the site as the FQDN set in the host headers bindings for this site/ip/port, I cannot get past the login prompt. Clicking cancel generates a http 401.1 error page.



and the answer for this one is going to be a security feature known as the authentication loopback check, introduced way back in Windows 2003 SP1, as per: http://support.microsoft.com/kb/926642

i was trying to connect to my iis host headers instance using a host header defined in my /etc/hosts file as pointing to, while logged in at the machine running iis - this is the loopback scenario.

it bites you in various contexts, such as this (http://blogs.bluethreadinc.com/thellebuyck/archive/2008/10/30/401.1-error-when-accessing-sharepoint-from-server.aspx) or this world of hurt in google (http://www.google.ca/search?q=authentication+loopback+check&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a)

THE FIX involves some simple regedit work: http://blogs.bluethreadinc.com/thellebuyck/archive/2008/10/30/401.1-error-when-accessing-sharepoint-from-server.aspx

i also did not need to enable impersonation for my situation, and so i disabled that, and now i can connect using my faked fqdn both locally and remotely