def unauthenticated_userid(request):
    """ Return the *unauthenticated* userid.  This method
        performs the same duty as ``authenticated_userid`` but is
        permitted to return the userid based only on data present
        in the request; it needn't (and shouldn't) check any
        persistent store to ensure that the user record related to
        the request userid exists.

        This method is intended primarily a helper to assist the
        ``authenticated_userid`` method in pulling credentials out
        of the request data, abstracting away the specific headers,
        query strings, etc that are used to authenticate the request.

        """
