Apache reverse-proxy application

Question

I have a reverse proxy configured to access an internal app from an external one. The internal application is accessed by passing an encrypted parameter: the user's ID.

Now my requirement is the following: I have to make another reverse proxy through this which will be accessed via the already configured proxy application. And I also need to make sure the second application can take this encrypted ID as parameter.

I am not big on Apache proxying. So I am uncertain if the direct authentication can be achieved in the second proxy via the first one. Any ideas will be helpful.