allow specific extension in forms authentication

I am using forms authentication with

<authorization>
  <deny users="?" />
</authorization>

However, I want to allow all calls made for specific extension say *.abc.

I tried:

<location path=".abc">
<system.web>
  开发者_C百科<authorization>
    <allow users="*"/>
  </authorization>
</system.web>

but wildcards are not allowed.

How can I allow *.abc calls to work for all users? Is there any web.config element I can use OR anything I can do in AuthenticateRequest httpmodule?

---

If it is a single file then you can do as following

<location path="filename.abc">

Otherwise put the files in folder/sub folder architecture and allow them for the anonymous use.

<location path="foldername">