app = FastAPI()


class FormModel(BaseModel):
    username: str
    lastname: str
    age: int | None = None
    tags: list[str] = ["foo", "bar"]
    alias_with: str = Field(alias="with", default="nothing")


class FormModelExtraAllow(BaseModel):
    param: str

    model_config = {"extra": "allow"}


@app.post("/form/")
def post_form(user: Annotated[FormModel, Form()]):
    return user