It can be used by the frontend team (that can also be yourself).

It can be used by third party applications and systems.

And it can also be used by yourself, to debug, check and test the same application.

## The `password` flow

Now let's go back a bit and understand what is all that.

## Einfach und leistungsstark

Obwohl das hierarchische Dependency Injection System sehr einfach zu definieren und zu verwenden ist, ist es dennoch sehr mächtig.

Sie können Abhängigkeiten definieren, die selbst wiederum Abhängigkeiten definieren können.

مشخصه OpenAPI روشی برای تعریف چندین "schemes" دارد.

با استفاده از آن‌ها، شما می‌توانید از همه این ابزارهای مبتنی بر استاندارد استفاده کنید، از جمله این سیستم‌های مستندات تعاملی(interactive documentation systems).

استاندارد OpenAPI شیوه‌های امنیتی زیر را تعریف می‌کند:

* شیوه `apiKey`: یک کلید اختصاصی برای برنامه که می‌تواند از موارد زیر استفاده شود:
    * پارامتر جستجو.
    * هدر.
    * کوکی.

It's relatively tightly coupled with relational databases (like MySQL or PostgreSQL), so, having a NoSQL database (like Couchbase, MongoDB, Cassandra, etc) as the main store engine is not very easy.

# About FastAPI versions

**FastAPI** is already being used in production in many applications and systems. And the test coverage is kept at 100%. But its development is still moving quickly.

New features are added frequently, bugs are fixed regularly, and the code is still continuously improving.

By using them, you can take advantage of all these standard-based tools, including these interactive documentation systems.

OpenAPI defines the following security schemes:

* `apiKey`: an application specific key that can come from:
    * A query parameter.
    * A header.
    * A cookie.
* `http`: standard HTTP authentication systems, including:

### Types and validation

These environment variables can only handle text strings, as they are external to Python and have to be compatible with other programs and the rest of the system (and even with different operating systems, as Linux, Windows, macOS).

That means that any value read in Python from an environment variable will be a `str`, and any conversion to a different type or validation has to be done in code.

* The **file** that can be **executed** by the operating system, for example: `python`, `python.exe` or `uvicorn`.
* A particular program while it is **running** on the operating system, using the CPU, and storing things on memory. This is also called a **process**.

### What is a Process

The word **process** is normally used in a more specific way, only referring to the thing that is running in the operating system (like in the last point above):

You actually don't have users that log in to your application but robots, bots, or other systems, that have just an access token? Again, it all works the same.

Just use any kind of model, any kind of class, any kind of database that you need for your application. **FastAPI** has you covered with the dependency injection system.

## Code size

    * All this would also work for deeply nested JSON objects.
* Convert from and to JSON automatically.
* Document everything with OpenAPI, that can be used by:
    * Interactive documentation systems.
    * Automatic client code generation systems, for many languages.
* Provide 2 interactive documentation web interfaces directly.

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We just scratched the surface, but you already get the idea of how it all works.