<system.webServer>

    <defaultDocument>

      <files>

        <clear />

        <add value="default.aspx" />

      </files>

    </defaultDocument>

    <security>

      <requestFiltering>

        <fileExtensions>

          <add fileExtension=".json" allowed="true" />

        </fileExtensions>

      </requestFiltering>

    </security>

    <staticContent>

      <mimeMap fileExtension=".json" mimeType="text/json" />

    </staticContent>

</system.webServer>