Config file web.config with System.Configuration ?

 Hi all!
I write a application for configure file web.config
Configuration config = WebConfigurationManager.OpenWebConfiguration("/" + appPath);
In file web.config

...<authorization>     
      <deny users="?"/>     
</authorization>
...
I need to set authorization from <deny users="?"/> to <allow users="*"/> in this application.

How can I do? 
Please, help me!
Thanks!

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