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


@app.post("/form-extra-allow/")
def post_form_extra_allow(params: Annotated[FormModelExtraAllow, Form()]):
    return params


client = TestClient(app)