Use REQUEST variable as dynamic upload location How can I use a request variable used in an upload form like this?

&lt;form method="post" accept-charset="UTF-8" enctype="multipart/form-data"&gt;
&lt;input type="hidden" name="action" value="entries/saveEntry"&gt;
&lt;input type="hidden" name="sectionId" value="29"&gt;
&lt;input type="hidden" name="enabled" value="1"&gt;
&lt;input type="file" name="fields[useruploads]"&gt;
&lt;input type="text" name="challenge_id"&gt;
...


The idea is to use the field "challenge_id" as dynamic upload location.



Is there a way to get this?
That field accepts any valid Twig code, so something like this should work:

challenges/{{ craft.request.getPost('challenge_id') }}/


Fair warning, though... I'd also be wary of accepting untrusted front-end input like this that ends up on the file system.