[Bug] Auth.current_user hangs when connected to WiFi but don't have internet

### [REQUIRED] Please fill in the following fields:

* Pre-built SDK from the [website](https://firebase.google.com/download/cpp) or open-source from this repo: open-source
* Firebase C++ SDK version: latest?
* Problematic Firebase Component: Auth
* Other Firebase Components in use: Firestore
* Platform you are using the C++ SDK on: Windows
* Platform you are targeting: desktop

### [REQUIRED] Please describe the issue here:

If you're connected to a WiFi that doesn't have internet, like at the airport or coffee shop (Starbucks is one), the `Auth.current_user` call hangs indefinitely.

#### Steps to reproduce:

Have you been able to reproduce this issue with just the [Firebase C++ quickstarts](https://github.com/firebase/quickstart-cpp) ? I didn't try before i left the repro environment

What's the issue repro rate? 100%

What happened? How can we make the problem occur?
This could be a description, log/console output, etc.

If you set Arc as your default browser and try to connect to a WiFi that doesn't have internet, it will hang until connected to internet.

This issue doesn't reproduce simply when not connected to internet. Which is very problematic for a browser where folks need to authenticate to the WiFi before they can get internet.

If you have a downloadable sample project that reproduces the bug you're reporting, you will
likely receive a faster response on your issue.

https://releases.arc.net/windows/ArcInstaller.exe

#### Relevant Code:

`auto user = Auth.current_user()`

Start by reproducing the hang in the Firebase C++ quickstarts on Windows with WiFi access but no internet, using the Auth.current_user call described in the issue. Compare this with the behavior when fully offline and inspect the Auth component's relevant entry points. Done means the call no longer hangs indefinitely in the captive-portal scenario and the regression is covered by a reproducible test.

索引モデルが issue の本文から書いたものです。