* `allow_credentials` - 指示跨域请求支持 cookies。默认是 `False`。另外，允许凭证时 `allow_origins` 不能设定为 `['*']`，必须指定源。
* `expose_headers` - 指示可以被浏览器访问的响应头。默认为 `[]`。
* `max_age` - 设定浏览器缓存 CORS 响应的最长时间，单位是秒。默认为 `600`。

中间件响应两种特定类型的 HTTP 请求……

### CORS 预检请求

这是些带有 `Origin` 和 `Access-Control-Request-Method` 请求头的 `OPTIONS` 请求。

* `allow_methods` - 교차-출처 요청을 허용하는 HTTP 메소드의 리스트입니다. 기본값은 `['GET']` 입니다. `['*']` 을 사용하여 모든 표준 메소드들을 허용할 수 있습니다.
* `allow_headers` - 교차-출처를 지원하는 HTTP 요청 헤더의 리스트입니다. 기본값은 `[]` 입니다. 모든 헤더들을 허용하기 위해 `['*']` 를 사용할 수 있습니다. `Accept`, `Accept-Language`, `Content-Language` 그리고 `Content-Type` 헤더는 CORS 요청시 언제나 허용됩니다.
* `allow_credentials` - 교차-출처 요청시 쿠키 지원 여부를 설정합니다. 기본값은 `False` 입니다. 또한 해당 항목을 허용할 경우 `allow_origins` 는 `['*']` 로 설정할 수 없으며, 출처를 반드시 특정해야 합니다.

* `allow_methods` - オリジン間リクエストで許可するHTTPメソッドのリスト。デフォルトは `['GET']` です。`['*']`を使用してすべての標準メソッドを許可できます。
* `allow_headers` - オリジン間リクエストでサポートするHTTPリクエストヘッダーのリスト。デフォルトは `[]` です。`['*']`を使用して、すべてのヘッダーを許可できます。CORSリクエストでは、 `Accept` 、 `Accept-Language` 、 `Content-Language` 、 `Content-Type` ヘッダーが常に許可されます。
* `allow_credentials` - オリジン間リクエストでCookieをサポートする必要があることを示します。デフォルトは `False` です。
* `expose_headers` - ブラウザからアクセスできるようにするレスポンスヘッダーを示します。デフォルトは `[]` です。

If an incoming request does not validate correctly then a `400` response will be sent.

## `GZipMiddleware`

Handles GZip responses for any request that includes `"gzip"` in the `Accept-Encoding` header.

The middleware will handle both standard and streaming responses.

```Python hl_lines="2  6"
{!../../../docs_src/advanced_middleware/tutorial003.py!}
```

The following arguments are supported:

            - cookies
            - client
            - state
            - url_for
            - client_state
            - application_state
            - receive
            - send
            - accept
            - receive_text
            - receive_bytes
            - receive_json
            - iter_text
            - iter_bytes
            - iter_json
            - send_text
            - send_bytes

In Python 3.6 and above (including Python 3.10) you can use the `Union` type from `typing` and put inside the square brackets the possible types to accept.

In Python 3.10 there's also a **new syntax** where you can put the possible types separated by a <abbr title='also called "bitwise or operator", but that meaning is not relevant here'>vertical bar (`|`)</abbr>.

Of course, the idea here is that everyone would access the app through the proxy, so the version with the path prefix `/api/v1` is the "correct" one.

And the version without the path prefix (`http://127.0.0.1:8000/app`), provided by Uvicorn directly, would be exclusively for the _proxy_ (Traefik) to access it.

# `Request` class

You can declare a parameter in a *path operation function* or dependency to be of type `Request` and then you can access the raw request object directly, without any validation, etc.

You can import it directly from `fastapi`:

```python
from fastapi import Request
```

!!! tip

Or you could also pin it with:

```txt
fastapi>=0.45.0,<0.46.0
```

that would mean that you would use the versions `0.45.0` or above, but less than `0.46.0`, for example, a version `0.45.2` would still be accepted.

If you use any other tool to manage your installations, like Poetry, Pipenv, or others, they all have a way that you can use to define specific versions for your packages.

## Available versions

Because of this, **FastAPI** itself provides an alternative API documentation (using ReDoc), which you can access at <a href="http://127.0.0.1:8000/redoc" class="external-link" target="_blank">http://127.0.0.1:8000/redoc</a>:

<img src="/img/tutorial/path-params/image02.png">