# Simple OAuth2 with Password and Bearer

Now let's build from the previous chapter and add the missing parts to have a complete security flow.

## Get the `username` and `password`

We are going to use **FastAPI** security utilities to get the `username` and `password`.

OAuth2 specifies that when using the "password flow" (that we are using) the client/user must send a `username` and `password` fields as form data.

    In particular, when running on **Kubernetes** you will probably **not** want to use Gunicorn and instead run **a single Uvicorn process per container**, but I'll tell you about it later in that chapter.

## Gunicorn with Uvicorn Workers

!!! info
    In this example we use invented custom headers `X-Key` and `X-Token`.

    But in real cases, when implementing security, you would get more benefits from using the integrated [Security utilities (the next chapter)](../security/index.md){.internal-link target=_blank}.

## Dependencies errors and return values

You can use the same dependency *functions* you use normally.

### Dependency requirements

    Data from forms is normally encoded using the "media type" `application/x-www-form-urlencoded`.

    But when the form includes files, it is encoded as `multipart/form-data`. You'll read about handling files in the next chapter.

To see all the options you have, checkout the docs for <a href="https://docs.pydantic.dev/latest/concepts/types/" class="external-link" target="_blank">Pydantic's exotic types</a>. You will see some examples in the next chapter.

For example, as in the `Image` model we have a `url` field, we can declare it to be an instance of Pydantic's `HttpUrl` instead of a `str`:

=== "Python 3.10+"

    ```Python hl_lines="2  8"

And that function takes parameters in the same way that *path operation functions* do.

!!! tip
    You'll see what other "things", apart from functions, can be used as dependencies in the next chapter.

Whenever a new request arrives, **FastAPI** will take care of:

* Calling your dependency ("dependable") function with the correct parameters.
* Get the result from your function.

   to use a memory-hard function (Argon2) that (on purpose) consumes a lot of memory and CPU.
   The new KMS-based approach can use a key derivation function that is orders of magnitudes
   cheaper w.r.t. memory and CPU.
- Root credentials can now be changed easily. Before, a two-step process was required to
   change the cluster root credentials since they were used to en/decrypt the IAM data.

!!! tip

    }
  }
}

suspend fun main() {
  val client = OkHttpClient()

  val scraper = SslLabsScraper(client)

  println(scraper.query())

  client.connectionPool.evictAll()
  client.dispatcher.executorService.shutdown()

That defines the metadata about the main response of a *path operation*.

You can also declare additional responses with their models, status codes, etc.

There's a whole chapter here in the documentation about it, you can read it at [Additional Responses in OpenAPI](additional-responses.md){.internal-link target=_blank}.

## OpenAPI Extra