Open up web.config and add the following just before the closing system.webServer to force HTTPS in beautiful IIS.

redirect.xml

<rewrite>
  <rules>
    <rule name="HTTP to HTTPS redirect" stopProcessing="true">
      <match url="(.*)" />
        <conditions>
          <add input="{HTTPS}" pattern="off" ignoreCase="true" />
        </conditions>
      <action type="Redirect" redirectType="Found" url="https://{HTTP_HOST}/{R:1}" />
    </rule>
  </rules>
</rewrite>