}
                                }
                            },
                        },
                    },
                    "summary": "Save Union Body",
                    "operationId": "save_union_body_items__post",
                    "requestBody": {
                        "content": {
                            "application/json": {
                                "schema": {

                                    }
                                }
                            },
                        },
                    },
                    "summary": "Save Item No Body",
                    "operationId": "save_item_no_body_items__item_id__put",
                    "parameters": [
                        {
                            "required": True,

                                    }
                                }
                            },
                        },
                    },
                    "summary": "Save Union Different Body",
                    "operationId": "save_union_different_body_items__post",
                    "requestBody": {
                        "content": {
                            "application/json": {

        self.name = name
        self.call = call
        self.use_cache = use_cache
        # Store the path to be able to re-generate a dependable from it in overrides
        self.path = path
        # Save the cache key at creation to optimize performance

That information is available in the app's **OpenAPI schema**, and then shown in the API docs (by Swagger UI).

And that same information from the models that is included in OpenAPI is what can be used to **generate the client code**.

### Generate a TypeScript Client

Now that we have the app with the models, we can generate the client code for the frontend.

#### Install `openapi-ts`

You will see that every language has all the pages. But some pages are not translated and have an info box at the top, about the missing translation.

Now let's say that you want to add a translation for the section [Features](features.md){.internal-link target=_blank}.

* Copy the file at:

```
docs/en/docs/features.md
```

* Paste it in exactly the same location but for the language you want to translate, e.g.:

```

                                    }
                                }
                            },
                        },
                    },
                    "summary": "Save Item No Body",
                    "operationId": "save_item_no_body_items__post",
                    "requestBody": {
                        "content": {
                            "application/json": {
                                "schema": {

# 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**.

query_extractor --> query_or_cookie_extractor --> read_query
```

## Using the same dependency multiple times

If one of your dependencies is declared multiple times for the same *path operation*, for example, multiple dependencies have a common sub-dependency, **FastAPI** will know to call that sub-dependency only once per request.

Whenever you pass exactly the same content (exactly the same password) you get exactly the same gibberish.

But you cannot convert from the gibberish back to the password.

### Why use password hashing

If your database is stolen, the thief won't have your users' plaintext passwords, only the hashes.