}

    public void setHeaders(final Map<String, List<String>> headers) {
        if (headers != null) {
            final Map<String, List<String>> map = new HashMap<>();
            headers.entrySet().stream().filter(e -> e.getKey() != null)
                    .forEach(e -> map.put(e.getKey().toLowerCase(Locale.ROOT), e.getValue()));
            this.headers = map;
        }
    }

```

////

/// warning

Before setting `convert_underscores` to `False`, bear in mind that some HTTP proxies and servers disallow the usage of headers with underscores.

///

## Duplicate headers

It is possible to receive duplicate headers. That means, the same header with multiple values.

You can define those cases using a list in the type declaration.

    assert response.headers["content-type"] == json_type


def test_router_a_a_override():
    with client:
        response = client.get("/a/a/override")
    assert response.content == b"Hello A A"
    assert response.headers["content-type"] == text_type


def test_router_a_b():
    with client:
        response = client.get("/a/b")
    assert response.content == b"Hello A B"

    response = client.get("/users/me", headers={"Authorization": "Bearer nonexistent"})
    assert response.status_code == 401, response.text
    assert response.json() == {"detail": "Invalid authentication credentials"}
    assert response.headers["WWW-Authenticate"] == "Bearer"


@needs_py310
def test_incorrect_token_type(client: TestClient):
    response = client.get(
        "/users/me", headers={"Authorization": "Notexistent testtoken"}

    response = client.get("/users/me", headers={"Authorization": "Bearer nonexistent"})
    assert response.status_code == 401, response.text
    assert response.json() == {"detail": "Invalid authentication credentials"}
    assert response.headers["WWW-Authenticate"] == "Bearer"


@needs_py310
def test_incorrect_token_type(client: TestClient):
    response = client.get(
        "/users/me", headers={"Authorization": "Notexistent testtoken"}

    response = client.get("/users/me", headers={"Authorization": "Bearer nonexistent"})
    assert response.status_code == 401, response.text
    assert response.json() == {"detail": "Could not validate credentials"}
    assert response.headers["WWW-Authenticate"] == 'Bearer scope="me"'


def test_incorrect_token_type():
    response = client.get(
        "/users/me", headers={"Authorization": "Notexistent testtoken"}
    )

```

////

**FastAPI** will **extract** the data for **each field** from the **headers** in the request and give you the Pydantic model you defined.

## Check the Docs

You can see the required headers in the docs UI at `/docs`:

<div class="screenshot">
<img src="/img/tutorial/header-param-models/image01.png">
</div>

## Forbid Extra Headers

    assert response.json() == {"detail": "Not authenticated"}
    assert response.headers["WWW-Authenticate"] == "Bearer"


@needs_py310
def test_token(client: TestClient):
    access_token = get_access_token(scope="me", client=client)
    response = client.get(
        "/users/me", headers={"Authorization": f"Bearer {access_token}"}
    )
    assert response.status_code == 200, response.text

    assert response.json() == {"detail": "Not authenticated"}
    assert response.headers["WWW-Authenticate"] == "Bearer"


@needs_py39
def test_token(client: TestClient):
    access_token = get_access_token(scope="me", client=client)
    response = client.get(
        "/users/me", headers={"Authorization": f"Bearer {access_token}"}
    )
    assert response.status_code == 200, response.text

    response = client.get(
        "/items?token=jessica", headers={"X-Token": "fake-super-secret-token"}
    )
    assert response.status_code == 200
    assert response.json() == {
        "plumbus": {"name": "Plumbus"},
        "gun": {"name": "Portal Gun"},
    }


def test_items_with_no_token_jessica(client: TestClient):
    response = client.get("/items", headers={"X-Token": "fake-super-secret-token"})