To create the callback *path operation* use the same `APIRouter` you created above.

It should look just like a normal FastAPI *path operation*:

* It should probably have a declaration of the body it should receive, e.g. `body: InvoiceEvent`.
* And it could also have a declaration of the response it should return, e.g. `response_model=InvoiceEventReceived`.

It is quite an extensive specification and covers several complex use cases.

It includes ways to authenticate using a "third party".

That's what all the systems with "login with Facebook, Google, X (Twitter), GitHub" use underneath.

### OAuth 1 { #oauth-1 }

    The only difference with a regular dependency is that it can declare OAuth2
    scopes that will be integrated with OpenAPI and the automatic UI docs (by default
    at `/docs`).

    It takes a single "dependable" callable (like a function).

    Don't call it directly, FastAPI will call it for you.

    Read more about it in the

You send it a token and it returns an authenticated user.

This provider might be charging you per request, and calling it might take some extra time than if you had a fixed mock user for tests.

You probably want to test the external provider once, but not necessarily call it for every test that runs.

Deploying a **FastAPI** application is relatively easy.

## What Does Deployment Mean { #what-does-deployment-mean }

To **deploy** an application means to perform the necessary steps to make it **available to the users**.

For a **web API**, it normally involves putting it in a **remote machine**, with a **server program** that provides good performance, stability, etc, so that your **users** can **access** the application efficiently and without interruptions or problems.

  /**
   * This is mutable and order matters. By default, it contains [IPv4, IPv6]. Tests may manipulate
   * it to prefer IPv6.
   */
  private var dnsResults = listOf<InetAddress>()

  @BeforeEach
  internal fun setUp() {
    val inetAddresses = InetAddress.getAllByName("localhost")
    localhostIpv4 = inetAddresses.firstOrNull { it is Inet4Address }
      ?: throw TestAbortedException()

// It randomly fetches an IP via custom LookupHost function and dials it by the given dial
// function. LookupHost may implement an internal DNS caching implementation, lookupHost
// input if nil then net.DefaultResolver.LookupHost is used.
//
// It dials one by one and returns first connected `net.Conn`.
// If it fails to dial all IPs from cache it returns first error. If no baseDialFunc

                + " It is derived from the main artifact.");
    }

    @Override
    public String getBaseVersion() {
        return parent.getBaseVersion();
    }

    @Override
    public void setBaseVersion(String baseVersion) {
        throw new UnsupportedOperationException("Cannot change the version information for an attached artifact."
                + " It is derived from the main artifact.");
    }

```

///

* The `app` directory contains everything. And it has an empty file `app/__init__.py`, so it is a "Python package" (a collection of "Python modules"): `app`.
* It contains an `app/main.py` file. As it is inside a Python package (a directory with a file `__init__.py`), it is a "module" of that package: `app.main`.
* There's also an `app/dependencies.py` file, just like `app/main.py`, it is a "module": `app.dependencies`.

Then pass the parameter `deprecated=True` to `Query`:

{* ../../docs_src/query_params_str_validations/tutorial010_an_py310.py hl[19] *}

The docs will show it like this:

<img src="/img/tutorial/query-params-str-validations/image01.png">

## Exclude parameters from OpenAPI { #exclude-parameters-from-openapi }