Google Sign-In across seven Unity platforms, one API

Seven platforms, seven OAuth flows, one method

Google Sign-In is an interesting case study in platform fragmentation. The underlying protocol is the same — OAuth 2.0 — but every platform has its own approved flow:

• Android wants Google Play Services. Pass a Web Client ID, let Play Services pick up the Android Client ID from the keystore signature.
• iOS wants ASWebAuthenticationSession with a deep-link callback.
• macOS / UWP want the system browser, also with a deep link.
• Windows / Editor want a loopback HTTP server.
• WebGL wants the JavaScript implicit flow.

Each of these is its own SDK, with its own setup dance in Google Cloud Console. If you build all seven in isolation, you end up with seven ways to call SignIn() in your game — and seven sets of bugs.

We built Universal Google Sign-In to hide all of that behind a single method. Call UniversalGSignIn.Init(CLIENT_ID, OnReady) in Unity. Call UniversalGSignIn.SignIn(OnUser) when the user taps the button. The right flow runs on the right platform. You get the same GoogleUser struct back regardless.

What the integration looks like in practice

void Start() {
    UniversalGSignIn.Init(WEB_CLIENT_ID, ready => {
        if (ready && UniversalGSignIn.IsSignedIn()) {
            ShowHome(UniversalGSignIn.GetCurrentUserBasicProfile());
        } else {
            signInButton.SetActive(true);
        }
    });
}

public void OnSignInTapped() {
    UniversalGSignIn.SignIn(user => {
        if (!string.IsNullOrEmpty(user.error)) {
            ShowError(user.error);
            return;
        }
        ShowHome(user.basicProfile);
    });
}

That's the whole integration. The Init call can accept an optional urlScheme (for iOS / macOS / UWP), clientSecret (for loopback on desktop), and loopbackLink (to pick a free port). Everything else is auto-detected per platform.

What still requires per-platform work

We don't paper over everything. Google still needs you to create the right client IDs in the Cloud Console — Web for Android/WebGL, iOS for deep-link platforms, Desktop for loopback. And you still need to configure deep links in Unity if you target iOS / macOS / UWP.

But once that setup is done once, the code is the code. No #if UNITY_ANDROID branches. No separate user structs per platform.

Why we charge $4.99

The plugin is a one-time purchase. No subscriptions, no seat counts, no usage caps. $4.99 buys you the source on your disk, the rights to ship it, and the future updates. If the native SDKs change — and they do, every year — we absorb that work so your game build doesn't break.

The listing is here. Source for open inspection is on GitHub.

If your game needs Google authentication and you don't want to become an OAuth expert, that's the deal.