# Simple OAuth2 with Password and Bearer

Now let's build from the previous chapter and add the missing parts to have a complete security flow.

## Get the `username` and `password`

We are going to use **FastAPI** security utilities to get the `username` and `password`.

OAuth2 specifies that when using the "password flow" (that we are using) the client/user must send a `username` and `password` fields as form data.

Nils Lindemann <******@****.***> 1711822124 +0100

DoHyun Kim <******@****.***> 1712097443 +0900

Nils Lindemann <******@****.***> 1713469999 +0200

Nils Lindemann <******@****.***> 1713469999 +0200

index-01-swagger-ui-simple.png...

index-02-redoc-simple.png...

        baz="simple_exclude model2 baz",
    )


@app.get(
    "/simple_exclude_dict",
    response_model=Model2,
    response_model_exclude={"ref": {"bar"}},
)
def simple_exclude_dict():
    return {
        "ref": {
            "foo": "simple_exclude_dict model foo",
            "bar": "simple_exclude_dict model bar",
        },

        def read_items(id: Dict[str, Item]):
            pass  # pragma: no cover


def test_invalid_simple_list():
    with pytest.raises(AssertionError):
        app = FastAPI()

        @app.get("/items/{id}")
        def read_items(id: list):
            pass  # pragma: no cover


def test_invalid_simple_tuple():
    with pytest.raises(AssertionError):
        app = FastAPI()

        @app.get("/items/{id}")

* Share database connections.
* Enforce security, authentication, role requirements, etc.
* And many other things...

All these, while minimizing code repetition.

## First Steps

Let's see a very simple example. It will be so simple that it is not very useful, for now.

But this way we can focus on how the **Dependency Injection** system works.

### Create a dependency, or "dependable"

Let's first focus on the dependency.