Flask mock abstract classes when testing

Question

I'm using flask for my REST API. But currently, I have a problem with mocking providers. Let's take the example below. In this case, I'm trying to test route /auth, but I don't want to use the real firebase login service and I would mock the service by utilizing some abstract class. But how do I do that when not using class for routes? Should I pass it as a parameter for a function def login()?

Example of a route:

@app.route('/auth', methods=['POST'])
def login():
    firebase_service.login()

Example of a route test:

def test_auth_returns_200(self, client):
    # When
    response = client.post("/auth")

    # Then
    assert response.status_code == 200