Why would httpx not store cookies if a "set-cookie" header is present in the response?

[aaronsgithub]

In a FastAPI app, running on localhost, I have in one of my routes:

    response.set_cookie(
        **{
            "key": "refreshToken",
            "value": refresh_token,
            "httponly": True,
            "samesite": "lax",
            "secure": False,
            "domain": "localhost",
            "max_age": REFRESH_TOKEN_EXP,
        }
    )

In the browser, I see the "Set-Cookie" header in the response, and also the cookie being stored in Devtools in the Application Tab under Cookies.

In httpx, I have:

> client = httpx.Client(base_url="http://localhost:8000")
> data = {"username": "me@example.com", "password": "P@ssword123"}
> r = client.post("/auth/users/token", data=data)
> r.json()
{'access_token': 'eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMyIsImV4cCI6MTY5MjkyMDU3Mn0.xwW6Pylli6PAwau1rg03ckeKisdoUXLaN2-iwSSG8q8',
 'token_type': 'bearer'}
> r.headers
 Headers({'date': 'Thu, 24 Aug 2023 23:12:51 GMT', 'server': 'uvicorn', 'content-length': '161', 'content-type': 'application/json', 'set-cookie': 'refreshToken=JoMTnkWpCK1yLk4CjFy03A9J8Y2QNr1veoN9zMZJTVK53NcdKH5G5pShH3OmXm8k; Domain=localhost; HttpOnly; Max-Age=1814400; Path=/; SameSite=lax'})
> r.cookies
<Cookies[]>
> client.cookies
<Cookies[]>

The cookies are empty.

Can anyone help me understand why that might be?

Many thanks in advance 🫡

[euri10]

you may have the answer here: https://stackoverflow.com/questions/1134290/cookies-on-localhost-with-explicit-domain

[aaronsgithub]

Thank you! Using the information in that link, I find that it works after removing the "domain" key, or using a domain which contains two "." and mapping that domain in my hosts file.