But first, let's check some small concepts.

## In a hurry?

If you don't care about any of these terms and you just need to add security with authentication based on username and password *right now*, skip to the next chapters.

## OAuth2

OAuth2 is a specification that defines several ways to handle authentication and authorization.

It is quite an extensive specification and covers several complex use cases.

* Memory
* Previous steps before starting

You can use the same type declarations with `str`, `float`, `bool` and many other complex data types.

Several of these are explored in the next chapters of the tutorial.

## Order matters

When creating *path operations*, you can find situations where you have a fixed path.

Like `/users/me`, let's say that it's to get data about the current user.

    ```

!!! tip
    All this might seem contrived. And it might not be very clear how is it useful yet.

    These examples are intentionally simple, but show how it all works.

    In the chapters about security, there are utility functions that are implemented in this same way.

!!! tip
    All this might not seem as useful with these simple examples.

    But you will see how useful it is in the chapters about **security**.

!!! danger
    Never store user's plaintext passwords. Always store a "secure hash" that you can then verify.

    If you don't know, you will learn what a "password hash" is in the [security chapters](security/simple-oauth2.md#password-hashing){.internal-link target=_blank}.

## Multiple models

Here's a general idea of how the models could look like with their password fields and the places where they are used:

        listener.start(String.format("class %s", classDoc.getName()));
        try {
            Element chapter = parent.getOwnerDocument().createElement("chapter");
            parent.appendChild(chapter);
            chapter.setAttribute("id", classDoc.getId());
            descriptionRenderer.renderTo(classDoc, chapter);
            merge(classDoc, chapter);
        } finally {
            listener.finish();
        }
    }

!!! tip

    In particular, when running on **Kubernetes** you will probably **not** want to use Gunicorn and instead run **a single Uvicorn process per container**, but I'll tell you about it later in that chapter.

## Gunicorn with Uvicorn Workers

  <modelVersion>4.0.0</modelVersion>
  <parent>
    <groupId>org.sonatype.mavenbook.multi</groupId>
    <artifactId>simple-parent</artifactId>
  </parent>

  <artifactId>simple-webapp</artifactId>
  <name>Multi Chapter Simple Web Application Project</name>
  <dependencies>
    <dependency>
      <groupId>org.sonatype.mavenbook.multi</groupId>
      <artifactId>simple-weather</artifactId>
    </dependency>
  </dependencies>
  <build>