C# - POST Data To A Flex/Flash (mxml) Application?

I have Flex application requiring to filter users depending on there database groups. Depending on which group they are, the're is a config.xml file that is use to populate the swf.

Here is how I figure how to do this :
1. The client comes to a .aspx page with a form requiring a username and a password.
2. On the server side I confirm the user credential
3. Once the username/password is valid I redirect to the mxml file with the config.xml file in the html headers (post).

My problem comes when I need to get the post data from the http request. Let's say I have this code :

<mx:Application initialize="init()">

<mx:Script>
<![CDATA[
[code]...
How do I get the post data on the init() function.