tasks.add_task(bg, state)
    return state


@app.middleware("http")
async def middleware(request, call_next):
    response: StreamingResponse = await call_next(request)
    response.headers["x-state"] = json.dumps(state.copy())
    return response


client = TestClient(app)


def test_async_state():

main concepts you should probably keep in mind when deploying a **FastAPI** application (although most of it applies to any other type of web application).

You will see more details to keep in mind and some of the techniques to do it in the next sections. ✨...

And it should have an `access_token`, with a string containing our access token.

For this simple example, we are going to just be completely insecure and return the same `username` as the token.

!!! tip
    In the next chapter, you will see a real secure implementation, with password hashing and <abbr title="JSON Web Tokens">JWT</abbr> tokens.

    But for now, let's focus on the specific details we need.

=== "Python 3.10+"

        <span class="sponsor-badge">sponsor</span>
        <img class="sponsor-image" src="/img/sponsors/coherence-banner.png" />
      </a>
    </div>
    <div class="item">

!!! info
    If you are using containers, for example with Docker or Kubernetes, I'll tell you more about that in the next chapter: [FastAPI in Containers - Docker](docker.md){.internal-link target=_blank}.

## Environment Variables

!!! tip
    If you already know what "environment variables" are and how to use them, feel free to skip to the next section below.

        Doc(
            """
            The URL to use to load the ReDoc JavaScript.

            It is normally set to a CDN URL.
            """
        ),
    ] = "https://cdn.jsdelivr.net/npm/redoc@next/bundles/redoc.standalone.js",
    redoc_favicon_url: Annotated[
        str,
        Doc(
            """
            The URL of the favicon to use. It is normally shown in the browser tab.
            """

Next, it 🤖 takes the first task to finish (let's say, our "slow-file" 📝) and continues whatever it had to do with it.

    🚥 👆 ✔️ 🔗 ⏮️ `yield`, 🚪 📟 🔜 🏃 *⏮️* 🛠️.

    🚥 📤 🙆 🖥 📋 (📄 ⏪), 👫 🔜 🏃 *⏮️* 🌐 🛠️.

## ✍ 🛠️

✍ 🛠️ 👆 ⚙️ 👨‍🎨 `@app.middleware("http")` 🔛 🔝 🔢.

🛠️ 🔢 📨:

*  `request`.
* 🔢 `call_next` 👈 🔜 📨 `request` 🔢.
    * 👉 🔢 🔜 🚶‍♀️ `request` 🔗 *➡ 🛠️*.
    * ⤴️ ⚫️ 📨 `response` 🏗 🔗 *➡ 🛠️*.
* 👆 💪 ⤴️ 🔀 🌅 `response` ⏭ 🛬 ⚫️.

```Python hl_lines="8-9  11  14"

* `description`
* `deprecated`

Validations specific for strings:

* `min_length`
* `max_length`
* `pattern`

In these examples you saw how to declare validations for `str` values.