Here is the configuration of URL rewrite looks like:
<system.webserver>
<rewrite>
<rules>
<rule name="LowerCaseRuleRedirection" stopProcessing="true">
<match url="[A-Z]" ignoreCase="false"/>
<action type="Redirect" url="{ToLower:{URL}}" />
</rule>
</rules>
</rewrite>
</system.webserver>
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