include a WWW-Authenticate header.

        Ref: https://datatracker.ietf.org/doc/html/rfc9110#name-401-unauthorized

        For this, this method sends a custom challenge `APIKey`.
        """
        return HTTPException(
            status_code=HTTP_401_UNAUTHORIZED,
            detail="Not authenticated",
            headers={"WWW-Authenticate": "APIKey"},
        )

So, if your API user (the external developer) sends a request to *your API* to:

```
https://yourapi.com/invoices/?callback_url=https://www.external.org/events
```

with a JSON body of:

```JSON
{
    "id": "2expen51ve",
    "customer": "Mr. Richie Rich",
    "total": "9999"
}
```

# Request Body { #request-body }

When you need to send data from a client (let's say, a browser) to your API, you send it as a **request body**.

A **request** body is data sent by the client to your API. A **response** body is the data your API sends to the client.

Then, the browser will send an HTTP `OPTIONS` request to the `:80`-backend, and if the backend sends the appropriate headers authorizing the communication from this different origin (`http://localhost:8080`) then the `:8080`-browser will let the JavaScript in the frontend send its request to the `:80`-backend.

To achieve this, the `:80`-backend must have a list of "allowed origins".

        this.streamCloseTimeout = streamCloseTimeout;
    }

    /**
     * Sends a command to the process associated with the given session ID.
     * Uses finer-grained locking to avoid blocking other operations during I/O.
     *
     * @param sessionId unique identifier for the process session
     * @param command the command to send to the process
     * @throws JobNotFoundException if no process is found for the given session ID

            setup.setup(form -> {
                updateForm(fessConfig, form);
            });
        });
    }

    /**
     * Sends a test mail using the provided notification settings.
     *
     * @param form the mail form containing notification settings
     * @return HTML response after sending test mail
     */
    @Execute

    And this path operation will:

    * Send the invoice to the client.
    * Collect the money from the client.
    * Send a notification back to the API user (the external developer), as a callback.
        * At this point is that the API will somehow send a POST request to the
            external API with the notification of the invoice event
            (e.g. "payment successful").
    """

            // notification
            try {
                crawler.sendMail(infoMap);
            } catch (final Exception e) {
                logger.warn("Failed to send notification mail.", e);
            }

        }
    }

    /**
     * Sends email notification with crawling results and statistics.
     * The email contains detailed information about the crawling session including

///

## Await for messages and send messages { #await-for-messages-and-send-messages }

In your WebSocket route you can `await` for messages and send messages.

{* ../../docs_src/websockets/tutorial001_py39.py hl[48:52] *}

You can receive and send binary, text, and JSON data.

## Try it { #try-it }

If your file is named `main.py`, run your application with:

    And this path operation will:

    * Send the invoice to the client.
    * Collect the money from the client.
    * Send a notification back to the API user (the external developer), as a callback.
        * At this point is that the API will somehow send a POST request to the
            external API with the notification of the invoice event
            (e.g. "payment successful").
    """