So, the section with:

{% raw %}

```jinja
<a href="{{ url_for('read_item', id=id) }}">
```

{% endraw %}

...will generate a link to the same URL that would be handled by the *path operation function* `read_item(id=id)`.

For example, with an ID of `42`, this would render:

```html
<a href="/items/42">
```

## Templates and static files

    If you integrate your API with an OAuth2 provider, you will be able to authenticate and come back to the API docs with the acquired credentials. And interact with it using the real OAuth2 authentication.

    Swagger UI will handle it behind the scenes for you, but it needs this "redirect" helper.

### Create a *path operation* to test it

Now, to be able to test that everything works, create a *path operation*:

```Python hl_lines="36-38"

    @classmethod
    def __get_pydantic_json_schema__(
        cls, core_schema: CoreSchema, handler: GetJsonSchemaHandler
    ) -> JsonSchemaValue:
        return {"type": "string", "format": "binary"}

    @classmethod
    def __get_pydantic_core_schema__(
        cls, source: Type[Any], handler: Callable[[Any], CoreSchema]
    ) -> CoreSchema:
        return with_info_plain_validator_function(cls._validate)

# Security

There are many ways to handle security, authentication and authorization.

And it normally is a complex and "difficult" topic.

In many frameworks and systems just handling security and authentication takes a big amount of effort and code (in many cases it can be 50% or more of all the code written).

    sub_router_shutdown: bool = False


@pytest.fixture
def state() -> State:
    return State()


@pytest.mark.filterwarnings(
    r"ignore:\s*on_event is deprecated, use lifespan event handlers instead.*:DeprecationWarning"
)
def test_router_events(state: State) -> None:
    app = FastAPI()

    @app.get("/")
    def main() -> Dict[str, str]:
        return {"message": "Hello World"}

## Create a task function

Create a function to be run as the background task.

It is just a standard function that can receive parameters.

It can be an `async def` or normal `def` function, **FastAPI** will know how to handle it correctly.

In this case, the task function will write to a file (simulating sending an email).

And as the write operation doesn't use `async` and `await`, we define the function with normal `def`:

When deploying applications you will probably want to have some **replication of processes** to take advantage of **multiple cores** and to be able to handle more requests.

As you saw in the previous chapter about [Deployment Concepts](concepts.md){.internal-link target=_blank}, there are multiple strategies you can use.