def approve(self, peer_jid):
        """
        (Pre-)approve a subscription request from `peer_jid`.

        :param peer_jid: The peer to (pre-)approve.

        This sends a ``"subscribed"`` presence to the peer; if the peer has
        previously asked for a subscription, this will seal the deal and create
        the subscription.

        If the peer has not requested a subscription (yet), it is marked as
        pre-approved by the server. A future subscription request by the peer
        will then be confirmed by the server automatically.

        .. note::

            Pre-approval is an OPTIONAL feature in :rfc:`6121`. It is announced
            as a stream feature.
        """
        self.client.enqueue(
            stanza.Presence(type_=structs.PresenceType.SUBSCRIBED,
                            to=peer_jid)
        )