// For the mock, we just log it
        log.info("Mock sending notification: {} for resource: {}", eventType, resourceName);

        // Count how many registrations this affects
        int affectedRegistrations = 0;
        for (MockRegistration reg : registrations.values()) {

    ```

 [CustomTrustJava]: https://github.com/square/okhttp/blob/master/samples/guide/src/main/java/okhttp3/recipes/CustomTrust.java
 [CustomTrustKotlin]: https://github.com/square/okhttp/blob/master/samples/guide/src/main/java/okhttp3/recipes/kt/CustomTrust.kt
 [CertificatePinningJava]: https://github.com/square/okhttp/blob/master/samples/guide/src/main/java/okhttp3/recipes/CertificatePinning.java

The simplest FastAPI file could look like this:

{* ../../docs_src/first_steps/tutorial001.py *}

Copy that to a file `main.py`.

Run the live server:

<div class="termy">

```console
$ <font color="#4E9A06">fastapi</font> dev <u style="text-decoration-style:solid">main.py</u>

  <span style="background-color:#009485"><font color="#D3D7CF"> FastAPI </font></span>  Starting development server 🚀

It's difficult to convey emotion in text, use emojis to help. 😅

```

</div>

<details markdown="1">
<summary>A parancsról <code>uvicorn main:app --reload</code>...</summary>

A `uvicorn main:app` parancs a következőre utal:

* `main`: fájl `main.py` (a Python "modul").
* `app`: a `main.py`-ban a `app = FastAPI()` sorral létrehozott objektum.
* `--reload`: kód változtatás esetén újra indítja a szervert. Csak fejlesztés közben használandó.

</details>

### Ellenőrizd

A single HTTP call may require follow-up requests to be made to handle authentication challenges, redirects, and HTTP-layer timeouts. In such cases multiple connections, requests, and responses may be attempted. Follow-ups are another reason a single call may trigger multiple events of the same type.

![Events Diagram](../assets/images/******@****.***)

In this scenario of "fast food burgers with your crush", as there is a lot of waiting 🕙, it makes a lot more sense to have a concurrent system ⏸🔀⏯.

This is the case for most of the web applications.

Many, many users, but your server is waiting 🕙 for their not-so-good connection to send their requests.

And then waiting 🕙 again for the responses to come back.

The same way, you can define logic (code) that should be executed when the application is **shutting down**. In this case, this code will be executed **once**, **after** having handled possibly **many requests**.

# Behind a Proxy { #behind-a-proxy }

In many situations, you would use a **proxy** like Traefik or Nginx in front of your FastAPI app.

These proxies could handle HTTPS certificates and other things.

## Proxy Forwarded Headers { #proxy-forwarded-headers }

This would allow you to have a more fine-grained permission system, following the OAuth2 standard, integrated into your OpenAPI application (and the API docs).

OAuth2 with scopes is the mechanism used by many big authentication providers, like Facebook, Google, GitHub, Microsoft, X (Twitter), etc. They use it to provide specific permissions to users and applications.