A "middleware" is a function that works with every **request** before it is processed by any specific *path operation*. And also with every **response** before returning it.

* It takes each **request** that comes to your application.
* It can then do something to that **request** or run any needed code.
* Then it passes the **request** to be processed by the rest of the application (by some *path operation*).

    You could also use `from starlette.staticfiles import StaticFiles`.

    **FastAPI** provides the same `starlette.staticfiles` as `fastapi.staticfiles` just as a convenience for you, the developer. But it actually comes directly from Starlette.

### What is "Mounting"

"Mounting" means adding a complete "independent" application in a specific path, that then takes care of handling all the sub-paths.

!!! check
    Notice that the value your function received (and returned) is `3`, as a Python `int`, not a string `"3"`.

    So, with that type declaration, **FastAPI** gives you automatic request <abbr title="converting the string that comes from an HTTP request into Python data">"parsing"</abbr>.

## Data validation

The main thing you need to run a **FastAPI** application (or any other ASGI application) in a remote server machine is an ASGI server program like **Uvicorn**, this is the one that comes by default in the `fastapi` command.

There are several alternatives, including:

* <a href="https://www.uvicorn.org/" class="external-link" target="_blank">Uvicorn</a>: a high performance ASGI server.

!!! note "Technical Details"
    You could also use `from starlette.testclient import TestClient`.

    **FastAPI** provides the same `starlette.testclient` as `fastapi.testclient` just as a convenience for you, the developer. But it comes directly from Starlette.

!!! tip

We are already halfway there.

We just need to add a *path operation* for the user/client to actually send the `username` and `password`.

<img src="/img/deployment/https/https07.svg">

The client (browser) will know that the response comes from the correct server because it is using the cryptography they agreed using the **HTTPS certificate** before.

### Multiple Applications

But it's signed. So, when you receive a token that you emitted, you can verify that you actually emitted it.

That way, you can create a token with an expiration of, let's say, 1 week. And then when the user comes back the next day with the token, you know that user is still logged in to your system.

* <a href="https://github.com/Kludex/python-multipart" target="_blank"><code>python-multipart</code></a> - Követelmény ha <abbr title="converting the string that comes from an HTTP request into Python data">"parsing"</abbr>-ot akarsz támogatni, `request.form()`-al.

- <a href="https://github.com/Kludex/python-multipart" target="_blank"><code>python-multipart</code></a> - আপনি যদি ফর্ম সহায়তা করতে চান তাহলে প্রয়োজন <abbr title="converting the string that comes from an HTTP request into Python data">"parsing"</abbr>, `request.form()` সহ।
- <a href="https://pythonhosted.org/itsdangerous/" target="_blank"><code>itsdangerous</code></a> - `SessionMiddleware` সহায়তার জন্য প্রয়োজন।