IIS digest doesn't permit pass-though authentication of proxy requests

This article helps you resolve the problem where digest authentication fails when a client sends a request through a proxy to a site and Microsoft Internet Information Services (IIS) uses digest authentication.

Original product version:   Internet Information Services
Original KB number:   3050055

Symptoms

Consider the following scenario:

• IIS is configured to use digest authentication.
• The server receives a request with the Via HyperText Transfer Protocol (HTTP) header. (This behavior occurs if the client request is rerouted through a proxy.)
• The resource requested is protected by digest authentication.
• A child request is created in the IIS pipeline. For example, a request is sent for a directory's default document, and the URL that is sent has a slash (/) as the last character.

In this scenario, digest authentication fails and the server returns a 401 response.

Cause

For security reasons, requests routed through a proxy and for which a child request is created in the IIS pipeline, IIS can't trust the digest authentication.

Workaround

Configure the website to use a different kind of authentication. For example, use Windows Authentication or basic authentication over Transport Layer Security (TLS). If you can't, try the following methods:

• Have the client use a request URL including the file name after the last / character.
• Set the application pool's managed pipeline mode to Classic.
• Use the URL Rewrite module to rewrite the URL path from / to /filename.

To use the URL Rewrite module to work around this issue, configure the module as follows:

<system.webServer>
    <rewrite>
        <rules>
            <rule name="<a rule name>" enabled="false">
                <match url="(^$|.*/$)" />
                <action type="Rewrite" url="{R:0}<a file name that you want the users to access>" />
            </rule>
        </rules>
    </rewrite>
</system.webServer>