'Store the ``userid`` as ``repoze.who.userid``.
The identity to authenticated to :mod:`repoze.who`
will contain the given userid as ``userid``, and
provide all keyword arguments as additional identity
keys. Useful keys could be ``max_age`` or ``userdata``.'

def remember(self, request, userid, **kw):

    identifier = self._get_identifier(request)
    if (identifier is None):
        return []
    environ = request.environ
    identity = kw
    identity['repoze.who.userid'] = userid
    return identifier.remember(environ, identity)
