// psiBased
        (symbol.psi?.containingFile as? KtFile)?.let { ktFile ->
            with(analysisSession) {
                return ktFile.getFileSymbol()
            }
        }
        // descriptorBased
        val descriptor = symbol.containingSymbolOrSelf.getDescriptor()
        val ktFile = descriptor?.let(DescriptorToSourceUtils::getContainingFile) ?: return null
        with(analysisSession) {

    System.setErr(object : PrintStream(OutputStream.nullOutputStream()) {})
  }

  fun uninstall() {
    originalSystemOut.let {
      System.setOut(it)
    }
    originalSystemErr.let {
      System.setErr(it)
    }
  }

* 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.

# Security - First Steps

Let's imagine that you have your **backend** API in some domain.

And you have a **frontend** in another domain or in a different path of the same domain (or in a mobile application).

And you want to have a way for the frontend to authenticate with the backend, using a **username** and **password**.

We can use **OAuth2** to build that with **FastAPI**.

            },
            file
        )
    }

    private
    fun getBuildTimestampAsString() =
        buildTimestamp.get().let { timestampFormat.format(it) }

    private
    fun getBuildTimestampAsIsoString() =
        buildTimestamp.get().let { isoTimestampFormat.format(it) }

    private
    fun Logger.logBuildVersion() {
        lifecycle(
            "Version: ${version.get()} " +

你可以用作 TLS 终止代理的一些选项包括：

* Traefik（也可以处理证书更新）
* Caddy（也可以处理证书更新）
* Nginx
* HAProxy

## Let's Encrypt

在 Let's Encrypt 之前，这些 **HTTPS 证书** 由受信任的第三方出售。

过去，获得这些证书的过程非常繁琐，需要大量的文书工作，而且证书非常昂贵。

但随后 **<a href="https://letsencrypt.org/" class="external-link" target="_blank">Let's Encrypt</a>** 创建了。

它是 Linux 基金会的一个项目。 它以自动方式免费提供 **HTTPS 证书**。 这些证书可以使用所有符合标准的安全加密，并且有效期很短（大约 3 个月），因此**安全性实际上更好**，因为它们的生命周期缩短了。

### Include an `APIRouter` with a custom `prefix`, `tags`, `responses`, and `dependencies`

Now, let's imagine your organization gave you the `app/internal/admin.py` file.

It contains an `APIRouter` with some admin *path operations* that your organization shares between several projects.

    {!> ../../../docs_src/python_types/tutorial008.py!}
    ```

This means:

* The variable `prices` is a `dict`:
    * The keys of this `dict` are of type `str` (let's say, the name of each item).
    * The values of this `dict` are of type `float` (let's say, the price of each item).

#### Union

You can declare that a variable can be any of **several types**, for example, an `int` or a `str`.

        @OptIn(UnresolvedExpressionTypeAccess::class)
        withClassEntry("coneTypeOrNull", annotation.coneTypeOrNull)
        @OptIn(UnsafeExpressionUtility::class)
        annotation.toReferenceUnsafe()?.let { withClassEntry("calleeReference", it) }
    }

    return annotation.argumentMapping.mapping.mapKeys { (name, _) -> name }
}

internal fun annotationsByClassId(
    firSymbol: FirBasedSymbol<*>,

                    .let(::FqName)
            }
        }
    }

    private fun collectTypeReferences(qualified: KtUserType): MutableList<KtNameReferenceExpression> {
        val refs = mutableListOf<KtNameReferenceExpression>()
        fun collectFragments(type: KtUserType) {
            type.getStubOrPsiChild(KtStubElementTypes.USER_TYPE)?.let { collectFragments(it) }