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1. Add the filter using the Internet Services Manager MMC console. Right click on the machine icon on the left, and edit the WWW Service master properties. On the "ISAPI Filters" tab, add a new filter called Shibboleth and specify the libexeclib\shibboleth\isapi_shib.dll library (or lib64\shibboleth\isapi_shib.dll for a 64-bit IIS). The priority should be High, and once the filter is loaded, make sure it appears in the list below the sspifilt entry. Restart IIS and make sure the filter shows up with a green arrow. Check the Windows event log and/or the Shibboleth logs if it fails to load.
2. Map the .sso file extension to the ISAPI library so that virtual URLs can be specified to invoke the extension handler for each web site. Right click on the machine icon on the left, and edit the WWW Service master properties. On the Home Directory tab, add a script mapping using the Configuration button. The Executable box should point to isapi_shib.dll, and the "Extension" can be set to anything unlikely to conflict, but .sso is assumed (and the dot must be included). You should NOT select the option to limit verbs, and you MUST uncheck the Check that file exists box.
3. Restart IIS.

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