lost User session when back from REST web service..

Once logged in and authenticated (using Authlogic), a user in my app
can upload a media file into a Remote Media Server , using a form. In
the form there is an url back upon success.

Fine, the file uploads correctly, the url_back is used upon success
and parameters are passed back (media_id)
but... the session is lost

so I wrote a before_filter :
  before_filter :require_user, :except => [:success, :failed]

in this case I lost the current_user.... (not abig deal as the :id is
passed back in the parameters

Is it normal to loose the session ? or did I miss anything prior
calling the remote server ?

thanks for your info

Yves