Bug report: Race condition in Flutter SDK `createOAuth2Session` / `client_io.dart

Hi team,

I've found an intermittent bug in the Flutter SDK (v20.3.0) when using createOAuth2Session on Android.

Symptoms

After createOAuth2Session resolves, an immediate call to _account.get() intermittently throws:

Root cause

In client_io.dart, the webAuth method resolves the Future immediately after:

_cookieJar.saveFromResponse(Uri.parse(_endPoint), cookies);

saveFromResponse is an async write operation that may not have fully persisted the session cookies by the time the caller makes the next API call. This creates a race condition between cookie persistence and subsequent authenticated requests.

Reproduction

• Android device
• OAuth2 provider: Google
• Call createOAuth2Session followed immediately by _account.get()
• Intermittent in debug mode, less frequent in release mode

Workaround

Retry _account.get() with exponential backoff after a 401 response.

Suggested fix

Ensure saveFromResponse is fully awaited and the cookie jar is flushed before resolving the Future in webAuth.