Allow callable auth to return generators

[mshober]

I would like my callable auth to be able to return generators just like httpx.Auth.auth_flow does, like this for example

from functools import cache
import httpx


class ApiClient:
    def __init__(self, username: str, password: str):
        self.client = httpx.Client(base_url="https://example.com", auth=self._auth_flow)
        self.username = username
        self.password = password

    @cache
    def _authenticate(self):
        return self.get_oauth_token(username=self.username, password=self.password)

    def _auth_flow(self, request: httpx.Request):
        request.headers["Authorization"] = f"Bearer {self._authenticate()}"
        response: httpx.Response = yield request
        if response.status_code == 401:
            self._authenticate.cache_clear()
            request.headers["Authorization"] = f"Bearer {self._authenticate()}"
            yield request

    def get_oauth_token(self, username: str, password: str) -> str:
        response = self.client.post("oauth/token", auth=(username, password))
        return response.json()["access_token"]
 
    ...

This would allow my _auth_flow function to yield additional requests that need to be made. I'd rather not create a seperate subclass of httpx.Auth because the auth flow is specific to the ApiClient. Using an instance method also lets me utilize self.client which feels much cleaner than yielding explicit httpx.Request instances in my auth flow.