In this section the subscription flow is described. VerneMQ provides several hooks to intercept the subscription flow. The most important ones are the auth_on_subscribe and auth_on_subscribe_m5 hooks which act as an application level firewall granting or rejecting subscribe requests.
The auth_on_subscribe and auth_on_subscribe_m5 hooks allow your plugin to grant or reject subscribe requests sent by a client. They also makes it possible to rewrite the subscribe topic and qos. The auth_on_subscribe hook is specified in the Erlang behaviour auth_on_subscribe_hook and the auth_on_subscribe hook in the auth_on_subscribe_m5_hook behaviour available in the vernemq_dev repo.
The on_subscribe and on_subscribe_m5 hooks allow your plugin to get informed about an authorized subscribe request. The on_subscribe hook is specified in the Erlang behaviour on_subscribe_hook and the on_subscribe_m5 hook in the on_subscribe_m5_hook behaviour available in the vernemq_dev repo.
The on_unsubscribe and on_unsubscribe_m5 hooks allow your plugin to get informed about an unsubscribe request. They also allow you to rewrite the unsubscribe topic if required. The on_subscribe hook is specified in the Erlang behaviour on_unsubscribe_hook and the on_unsubscribe_m5 hook in the on_unsubscribe_m5_hook behaviour available in the vernemq_dev repo.