# OpenAPI

There are several utilities to handle OpenAPI.

    All the security utilities that integrate with OpenAPI (and the automatic API docs) inherit from `SecurityBase`, that's how **FastAPI** can know how to integrate them in OpenAPI.

## What it does

# OpenAPI `docs`

Utilities to handle OpenAPI automatic UI documentation, including Swagger UI (by default at `/docs`) and ReDoc (by default at `/redoc`).

::: fastapi.openapi.docs.get_swagger_ui_html

::: fastapi.openapi.docs.get_redoc_html

::: fastapi.openapi.docs.get_swagger_ui_oauth2_redirect_html

!!! info
    In this example we use invented custom headers `X-Key` and `X-Token`.

    But in real cases, when implementing security, you would get more benefits from using the integrated [Security utilities (the next chapter)](../security/index.md){.internal-link target=_blank}.

## Dependencies errors and return values

You can use the same dependency *functions* you use normally.

### Dependency requirements

    The most complex problem is building an authentication/authorization provider like those, but **FastAPI** gives you the tools to do it easily, while doing the heavy lifting for you.

## **FastAPI** utilities

FastAPI provides several tools for each of these security schemes in the `fastapi.security` module that simplify using these security mechanisms.

### In production

In your production system, you probably have a frontend created with a modern framework like React, Vue.js or Angular.

And to communicate using WebSockets with your backend you would probably use your frontend's utilities.

Or you might have a native mobile application that communicates with your WebSocket backend directly, in native code.

Or you might have any other way to communicate with the WebSocket endpoint.

---

# Templates

You can use any template engine you want with **FastAPI**.

A common choice is Jinja2, the same one used by Flask and other tools.

There are utilities to configure it easily that you can use directly in your **FastAPI** application (provided by Starlette).

## Install dependencies

Install `jinja2`:

<div class="termy">

```console
$ pip install jinja2

---> 100%
```

</div>

```

## Install custom exception handlers

You can add custom exception handlers with <a href="https://www.starlette.io/exceptions/" class="external-link" target="_blank">the same exception utilities from Starlette</a>.

Let's say you have a custom exception `UnicornException` that you (or a library you use) might `raise`.

And you want to handle this exception globally with FastAPI.

* Générer des définitions <a href="https://json-schema.org" class="external-link" target="_blank">JSON Schema</a> pour votre modèle, qui peuvent être utilisées où vous en avez besoin dans votre projet ensuite.
* Ces schémas participeront à la constitution du schéma généré OpenAPI, et seront donc utilisés par les documentations automatiquement générées.

## Documentation automatique

Dans OpenAPI, les chemins sont des ressources, tels que /users/ ou /items/, exposées par votre API, et les opérations sont les méthodes HTTP utilisées pour manipuler ces chemins, telles que GET, POST ou DELETE. Les operationId sont des chaînes uniques facultatives utilisées pour identifier une opération d'un chemin. Vous pouvez définir l'OpenAPI `operationId` à utiliser dans votre *opération de chemin* avec le paramètre `operation_id`.