web.config

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
  <system.webServer>
    <rewrite>
      <rules>
        <rule name="Convert to lower case" stopProcessing="true">
          <match url="[A-Z]" ignoreCase="false" />
          <action type="Redirect" url="{ToLower:{Url}}" redirectType="Permanent" />
        </rule>
      </rules>
    </rewrite>
  </system.webServer>
</configuration>