次の章では、FastAPIアプリケーションをデプロイするための**具体的なレシピ**を紹介します。

しかし、今はこれらの重要な**コンセプトに基づくアイデア**を確認しましょう。これらのコンセプトは、他のどのタイプのWeb APIにも当てはまります。💡

## セキュリティ - HTTPS

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[前チャプターのHTTPSについて](https.md){.internal-link target=_blank}では、HTTPSがどのようにAPIを暗号化するのかについて学びました。

通常、アプリケーションサーバにとって**外部の**コンポーネントである**TLS Termination Proxy**によって提供されることが一般的です。このプロキシは通信の暗号化を担当します。

    *extra_items: Union[DefaultPlaceholder, DefaultType],
) -> Union[DefaultPlaceholder, DefaultType]:
    """
    Pass items or `DefaultPlaceholder`s by descending priority.

    The first one to _not_ be a `DefaultPlaceholder` will be returned.

    Otherwise, the first item (a `DefaultPlaceholder`) will be returned.
    """
    items = (first_item,) + extra_items
    for item in items:

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.

In this case, you can override the dependency that calls that provider, and use a custom dependency that returns a mock user, only for your tests.

---

"_If you're looking to learn one **modern framework** for building REST APIs, check out **FastAPI** [...] It's fast, easy to use and easy to learn [...]_"

"_We've switched over to **FastAPI** for our **APIs** [...] I think you'll like it [...]_"

---

"_If you're looking to learn one **modern framework** for building REST APIs, check out **FastAPI** [...] It's fast, easy to use and easy to learn [...]_"

"_We've switched over to **FastAPI** for our **APIs** [...] I think you'll like it [...]_"

    * If you depended on that previous behavior,...

But once we create an instance of the `SessionLocal` class, this instance will be the actual database session.

We name it `SessionLocal` to distinguish it from the `Session` we are importing from SQLAlchemy.

We will use `Session` (the one imported from SQLAlchemy) later.

To create the `SessionLocal` class, use the function `sessionmaker`:

graph TB

common_parameters(["common_parameters"])
read_items["/items/"]
read_users["/users/"]

common_parameters --> read_items
common_parameters --> read_users
```

This way you write shared code once and **FastAPI** takes care of calling it for your *path operations*.

!!! check
    Notice that you don't have to create a special class and pass it somewhere to **FastAPI** to "register" it or anything similar.

* `seek(offset)`: Goes to the byte position `offset` (`int`) in the file.
    * E.g., `await myfile.seek(0)` would go to the start of the file.
    * This is especially useful if you run `await myfile.read()` once and then need to read the contents again.
* `close()`: Closes the file.

As all these methods are `async` methods, you need to "await" them.

You can define those cases using a list in the type declaration.

You will receive all the values from the duplicate header as a Python `list`.

For example, to declare a header of `X-Token` that can appear more than once, you can write:

=== "Python 3.10+"

    ```Python hl_lines="9"
    {!> ../../../docs_src/header_params/tutorial003_an_py310.py!}
    ```

=== "Python 3.9+"

    ```Python hl_lines="9"