How to secure an aspx page called by Flex?

How can I secure an aspx page that is called by a Flex application of ours? It has to be secured for the whole application, not for particular users.

Is it possible to give credentials with the Flex Call? In Asp.net, only some five aspx pages need to be secured. The amf calls are already secured.

I do not want a popup to be displayed when Flex calls the page. The users are not in Active Directory, so they wouldn't be able to log in开发者_如何学Python.

Examples of aspx pages we use from Flex are aspx pages to load media, to get an export of data in csv format, to upload media, ...