///

### Add the callback router { #add-the-callback-router }

At this point you have the *callback path operation(s)* needed (the one(s) that the *external developer*  should implement in the *external API*) in the callback router you created above.

Now use the parameter `callbacks` in *your API's path operation decorator* to pass the attribute `.routes` (that's actually just a `list` of routes/*path operations*) from that callback router:

* `summary`: A short summary of the API.
* `description`: The description of your API, this can include markdown and will be shown in the docs.
* `routes`: A list of routes, these are each of the registered *path operations*. They are taken from `app.routes`.

/// info

The parameter `summary` is available in OpenAPI 3.1.0 and above, supported by FastAPI 0.99.0 and above.

///

[providers]
  [providers.file]
    filename = "routes.toml"
```

This tells Traefik to listen on port 9999 and to use another file `routes.toml`.

/// tip

We are using port 9999 instead of the standard HTTP port 80 so that you don't have to run it with admin (`sudo`) privileges.

///

Now create that other file `routes.toml`:

```TOML hl_lines="5  12  20"
[http]
  [http.middlewares]

* There's a subdirectory `app/routers/` with another file `__init__.py`, so it's a "Python subpackage": `app.routers`.
* The file `app/routers/items.py` is inside a package, `app/routers/`, so, it's a submodule: `app.routers.items`.
* The same with `app/routers/users.py`, it's another submodule: `app.routers.users`.

* <a href="https://github.com/OAI/OpenAPI-Specification" class="external-link" target="_blank"><strong>OpenAPI</strong></a> for API creation, including declarations of <abbr title="also known as: endpoints, routes">path</abbr> <abbr title="also known as HTTP methods, as POST, GET, PUT, DELETE">operations</abbr>, parameters, request bodies, security, etc.

The dependency injection system requires pre-registration of the dependencies and the dependencies are solved based on the declared types. So, it's not possible to declare more than one "component" that provides a certain type.

		return matches[1]
	}
	return "unknown"
}

func methodNotAllowedHandler(api string) func(w http.ResponseWriter, r *http.Request) {
	return errorResponseHandler
}

// If none of the http routes match respond with appropriate errors
func errorResponseHandler(w http.ResponseWriter, r *http.Request) {
	if r.Method == http.MethodOptions {
		return
	}

func registerAPIFunctions(muxRouter *mux.Router, objLayer ObjectLayer, apiFunctions ...string) {
	if len(apiFunctions) == 0 {
		// Register all api endpoints by default.
		registerAPIRouter(muxRouter)
		return
	}
	// API Router.
	apiRouter := muxRouter.PathPrefix(SlashSeparator).Subrouter()
	// Bucket router.

{* ../../docs_src/custom_request_and_route/tutorial002.py hl[16:18] *}

## Custom `APIRoute` class in a router { #custom-apiroute-class-in-a-router }

You can also set the `route_class` parameter of an `APIRouter`:

{* ../../docs_src/custom_request_and_route/tutorial003.py hl[26] *}

    * PR [#589](https://github.com/tiangolo/fastapi/pull/589) by [@dmontagu](https://github.com/dmontagu).
* Fix preserving custom route class in routers when including other sub-routers. PR [#538](https://github.com/tiangolo/fastapi/pull/538) by [@dmontagu](https://github.com/dmontagu).

## 0.40.0