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I've got an Intranet site that uses Windows Authentication and is accessed through an IIS 7 Reverse Proxy. Using FireFox, Safari or Chrome it works fine. I'm prompted for credentials, I supply them and away I go. In IE 7/8 I get prompted for credentials but they're rejected and I eventually get a 401 not authorized error.

The application server is configured for Windows Auth only and rejects basic authentication. I would be surprised if the front end proxy would accept Basic Auth so my suspicion is that it's a trust issue with my browser and IE isn't relaying the credentials however our IS Team has IE so locked down I'm unable to alter trust levels or even view the settings.

How should I go about troubleshooting this problem? I'm at a loss and they've yet to respond to my support ticket.

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up vote 0 down vote accepted

It turns out that the IIS 7/7.5 proxy doesn't support proxying Kerberos. IE relays that it supports Kerberos so the proxied server attempts and fails to establish a Kerberos session where as other browsers use NTLM. Disabling Kerberos as a provider on the proxied server resolves the issue.

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