def test_union_scalar_list():
    # For coverage
    # TODO: there might not be a current valid code path that uses this, it would
    # potentially enable query parameters defined as both a scalar and a list
    # but that would require more refactors, also not sure it's really useful
    from fastapi._compat import is_pv1_scalar_field

    field_info = FieldInfo()
    field = ModelField(
        name="foo",
        field_info=field_info,

It has a `GET` operation that could return an error.

It has a `POST` operation that could return several errors.

Both *path operations* require an `X-Token` header.

=== "Python 3.10+"

    ```Python
    {!> ../../../docs_src/app_testing/app_b_an_py310/main.py!}
    ```

=== "Python 3.9+"

    ```Python

* Nginx
* HAProxy

## Let's Encrypt

Before Let's Encrypt, these **HTTPS certificates** were sold by trusted third parties.

The process to acquire one of these certificates used to be cumbersome, require quite some paperwork and the certificates were quite expensive.

But then **<a href="https://letsencrypt.org/" class="external-link" target="_blank">Let's Encrypt</a>** was created.

It gives you all the flexibility to choose the ones that fit your project the best.

And you can use directly many well maintained and widely used packages like `passlib` and `python-jose`, because **FastAPI** doesn't require any complex mechanisms to integrate external packages.

But it provides you the tools to simplify the process as much as possible without compromising flexibility, robustness, or security.

    * You can also add [`Security` dependencies with `scopes`](../advanced/security/oauth2-scopes.md){.internal-link target=_blank}.

!!! tip
    Having `dependencies` in the `APIRouter` can be used, for example, to require authentication for a whole group of *path operations*. Even if the dependencies are not added individually to each one of them.

!!! check

    grant_type: the OAuth2 spec says it is required and MUST be the fixed string "password".
        This dependency is strict about it. If you want to be permissive, use instead the
        OAuth2PasswordRequestForm dependency class.
    username: username string. The OAuth2 spec requires the exact field name "username".
    password: password string. The OAuth2 spec requires the exact field name "password".

```

Mais déclare explicitement `q` comme étant un paramètre de requête.

!!! info
    Gardez à l'esprit que la partie la plus importante pour rendre un paramètre optionnel est :

    ```Python
    = None
    ```

    ou :

    ```Python
    = Query(None)
    ```

    et utilisera ce `None` pour détecter que ce paramètre de requête **n'est pas requis**.

It requires a little bit more verbose configurations. And as it is based on WSGI (instead of ASGI), it is not designed to take advantage of the high performance provided by tools like Uvicorn, Starlette and Sanic.

                    "msg": "Field required",
                    "input": None,
                }
            ]
        }
    ) | IsDict(
        # TODO: remove when deprecating Pydantic v1
        {
            "detail": [
                {
                    "loc": ["body", "password"],
                    "msg": "field required",
                    "type": "value_error.missing",

                    "msg": "Field required",
                    "input": None,
                }
            ]
        }
    ) | IsDict(
        # TODO: remove when deprecating Pydantic v1
        {
            "detail": [
                {
                    "loc": ["query", "token"],
                    "msg": "field required",
                    "type": "value_error.missing",