> For the complete documentation index, see [llms.txt](https://courier-gojek.gitbook.io/vernemq/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://courier-gojek.gitbook.io/vernemq/plugin-development/subscribeflow.md).

# Subscribe Flow

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.

![](/files/fMyvRqeYcsfdmlgAdcDn)

## auth\_on\_subscribe and auth\_on\_subscribe\_m5

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](https://github.com/gojekfarm/vernemq_dev/blob/master/src/auth_on_subscribe_hook.erl) and the `auth_on_subscribe` hook in the [auth\_on\_subscribe\_m5\_hook](https://github.com/gojekfarm/vernemq_dev/blob/master/src/auth_on_subscribe_m5_hook.erl) behaviour available in the [vernemq\_dev](https://github.com/gojekfarm/vernemq_dev) repo.

## on\_subscribe and on\_subscribe\_m5

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](https://github.com/gojekfarm/vernemq_dev/blob/master/src/on_subscribe_hook.erl) and the `on_subscribe_m5` hook in the [on\_subscribe\_m5\_hook](https://github.com/gojekfarm/vernemq_dev/blob/master/src/on_subscribe_m5_hook.erl) behaviour available in the [vernemq\_dev](https://github.com/gojekfarm/vernemq_dev) repo.

## on\_unsubscribe and on\_unsubscribe\_m5

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](https://github.com/gojekfarm/vernemq_dev/blob/master/src/on_unsubscribe_hook.erl) and the `on_unsubscribe_m5` hook in the [on\_unsubscribe\_m5\_hook](https://github.com/gojekfarm/vernemq_dev/blob/master/src/on_unsubscribe_m5_hook.erl) behaviour available in the [vernemq\_dev](https://github.com/gojekfarm/vernemq_dev) repo.


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://courier-gojek.gitbook.io/vernemq/plugin-development/subscribeflow.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.