When `authenticate_user` is called with a username that doesn't exist in the database, we still run `verify_password` against a dummy hash.

This ensures the endpoint takes roughly the same amount of time to respond whether the username is valid or not, preventing **timing attacks** that could be used to enumerate existing usernames.

/// note

## `username`과 데이터 형태 검증하기 { #verify-the-username-and-data-shape }

`username`을 얻었는지 확인하고, 스코프를 추출합니다.

그런 다음 Pydantic 모델로 데이터를 검증합니다(`ValidationError` 예외를 잡습니다). JWT 토큰을 읽거나 Pydantic으로 데이터를 검증하는 과정에서 오류가 나면, 앞에서 만든 `HTTPException`을 raise합니다.

이를 위해 Pydantic 모델 `TokenData`에 새 속성 `scopes`를 추가합니다.

Pydantic으로 데이터를 검증하면, 예를 들어 스코프가 정확히 `str`의 `list`이고 `username`이 `str`인지 등을 보장할 수 있습니다.

        String username = null;
        FessUserNotFoundException exception = new FessUserNotFoundException(username);

        assertNotNull(exception);
        assertEquals("User is not found: null", exception.getMessage());
        assertNull(exception.getCause());
    }

    @Test
    public void test_constructor_withSpecialCharacters() {
        // Test with username containing special characters

    * It contains the `username` and `password` sent.

{* ../../docs_src/security/tutorial006_an_py310.py hl[4,8,12] *}

When you try to open the URL for the first time (or click the "Execute" button in the docs) the browser will ask you for your username and password:

<img src="/img/tutorial/security/image12.png">

## Check the username { #check-the-username }

Here's a more complete example.

def get_password_hash(password):
    return password_hash.hash(password)


def get_user(db, username: str):
    if username in db:
        user_dict = db[username]
        return UserInDB(**user_dict)


def authenticate_user(fake_db, username: str, password: str):
    user = get_user(fake_db, username)
    if not user:
        verify_password(password, DUMMY_HASH)
        return False

        }
    }
)


class User(BaseModel):
    username: str


# Here we use string annotations to test them
def get_current_user(oauth_header: "str" = Security(reusable_oauth2)):
    user = User(username=oauth_header)
    return user


@app.post("/login")
# Here we use string annotations to test them

        }
    },
    description="OAuth2 security scheme",
    auto_error=False,
)


class User(BaseModel):
    username: str


def get_current_user(oauth_header: str | None = Security(reusable_oauth2)):
    if oauth_header is None:
        return None
    user = User(username=oauth_header)
    return user


@app.post("/login")
def login(form_data: OAuth2PasswordRequestFormStrict = Depends()):

    class User(BaseModel):
        username: str
        role: PlatformRole | OtherRole

    @app.get("/users")
    async def get_user() -> User:
        return {"username": "alice", "role": "admin"}

    client = TestClient(app)
    return client


@needs_py310
def test_get(client: TestClient):
    response = client.get("/users")
    assert response.json() == {"username": "alice", "role": "admin"}

                    },
                    "User": {
                        "title": "User",
                        "required": ["username"],
                        "type": "object",
                        "properties": {
                            "username": {"title": "Username", "type": "string"},
                            "full_name": {
                                "title": "Full Name",

            status_code=status.HTTP_401_UNAUTHORIZED,
            detail="Incorrect username or password",
            headers={"WWW-Authenticate": "Basic"},
        )
    return credentials.username


@app.get("/users/me")
def read_current_user(username: str = Depends(get_current_username)):