client = Client() # will make unauthenticated requests
auth_client = AuthenticatedClient(token='my-token') # will make authenticated requests

auth_client1 = AuthenticatedClient(token='user1-token') # will make authenticated requests for user1
auth_client2 = AuthenticatedClient(token='user2-token') # will make authenticated requests for user2

client = Client()
client.with_authorization_token(token='user1-token')
client.request() # will make auth requests for user1
client.with_authorization_token(token='user2-token')

from base64 import b64encode
from typing import Dict, Generic, TypeVar, cast

from attrs import define, evolve, field


class Unauthenticated: ...


class Authenticated: ...


_State = TypeVar("_State")


@define
class _Client(Generic[_State]):
    _headers: Dict[str, str] = field(factory=dict, kw_only=True)

    def with_headers(self, headers: Dict[str, str]) -> "Client":
        return evolve(self, _headers={**self._headers, **headers})

    def with_authorization_token(
        self: "Client",
        token: str,
        prefix: str = "Bearer",
    ) -> "AuthClient":
        return cast("AuthClient", self.with_headers({"Authorization": f"{prefix} {token}"}))

    def with_authorization_basic(
        self: "Client",
        username: str,
        password: str,
        prefix: str = "Basic",
    ) -> "AuthClient":
        encoded_credentials = b64encode(f"{username}:{password}".encode()).decode()
        return cast("AuthClient", self.with_headers({"Authorization": f"{prefix} {encoded_credentials}"}))

    def remove_headers(self: "AuthClient") -> "Client":
        return evolve(self, _headers={})


Client = _Client[Unauthenticated]
AuthClient = _Client[Authenticated]


def my_func(client: AuthClient) -> None:
    # only accepts authenticated clients
    print("got headers:", client._headers)


# --- usage demos ---
c0 = Client()  # Unauthenticated
my_func(c0)  # static type error

c1 = c0.with_authorization_token("my-token")  # Authenticated
my_func(c1)  # ok

c2 = c1.remove_headers()  # back to Unauthenticated
my_func(c2)  # static type error

c1 = c0.with_authorization_basic("my-username", "my-password")  # Authenticated
my_func(c1)  # ok