TestClient does not support auth param

[mshober]

Related to #1914.

TestClient does not support the auth param, e.g.:

from starlette.testclient import TestClient
import httpx


class ApiClient:
    _client_class: type[httpx.Client] = httpx.Client

    def __init__(self) -> None:
        self._client = self._client_class(auth=self._auth_flow)

    @property
    def _credentials(self) -> str:
        return "REAL_CREDENTIALS"

    def _auth_flow(self, request: httpx.Request) -> httpx.Request:
        request.headers["Authorization"] = self._credentials
        return request
     
    ...
    
class FakeApiClient(ApiClient):
    _client_class = TestClient

    @property
    def _credentials(self) -> str:
        return "FAKE_CREDENTIALS"


fake_client = FakeApiClient() # TypeError: TestClient.__init__() got an unexpected keyword argument 'auth'

Any reason why that can't be added to TestClient.__init__()?

[Kludex]

This can be done with the headers parameter, can't it?

[mshober]

In this specific dumbed-down example yes, but headers won't work for more advanced cases like OAuth that involve more than one request.

[Kludex]

PR welcome.