Table of Contents

Credentials

To use Rust+ you need credentials. There are two kinds:

  • FCM credentials — identify your "device" to Google Firebase Cloud Messaging so you can receive Rust+ push notifications (used by RustPlusFcm).
  • Server pairing values — ip, port, playerId, playerToken for a specific server, sent to you as a push notification when you choose Pair with Server in game (used by RustPlus).

The RustPlusApi.Fcm.Registration package acquires both natively, replacing the rustplus.js Node CLI.

The flow

sequenceDiagram
    participant App as Your app
    participant G as Google (GCM/Firebase/FCM)
    participant E as Expo
    participant St as Steam (via Chrome)
    participant FP as Facepunch (Rust Companion)
    participant Game as Rust (in game)

    App->>G: 1. GCM check-in
    G-->>App: androidId + securityToken
    App->>G: 2-3. Firebase install + FCM register
    G-->>App: FCM token
    App->>E: 4. Expo push token
    E-->>App: ExponentPushToken[...]
    App->>St: 5. Interactive Steam login (Chrome DevTools)
    St-->>App: Steam auth token
    App->>FP: 6. Register device with Rust Companion
    FP-->>App: subscribed to pairing pushes
    Note over App: 7. CredentialsStore.Save("rustplus.config.json")
    Game->>FP: 8. "Pair with Server" in game
    FP->>G: push notification
    G-->>App: ServerPairing (ip/port/playerId/playerToken)

FcmRegistration orchestrates the whole chain:

using RustPlusApi.Fcm.Registration;

var registration = new FcmRegistration();

// Steps 1–4: GCM check-in → Firebase install → FCM register → Expo token.
var credentials = await registration.AcquireCredentialsAsync();

// Steps 5–6: interactive Steam login (launches Chrome) + Rust Companion device registration.
await registration.RegisterWithRustPlusAsync(credentials);

// Step 7: persist for later runs.
CredentialsStore.Save("rustplus.config.json", credentials);

// Step 8: pair in game; one await yields the RustPlus constructor args.
using var listener = new PairingListener(credentials);
ServerPairing pairing = await listener.WaitForServerPairingAsync();
// new RustPlus(new RustPlusConnection(pairing.Ip, pairing.Port, pairing.PlayerId, pairing.PlayerToken))
Step Component Result
1 AndroidFcmRegister.CheckInAsync Android id + security token
2 AndroidFcmRegister.InstallAsync Firebase installation token
3 AndroidFcmRegister.RegisterFcmAsync FCM token
4 ExpoPushClient.GetTokenAsync Expo push token
5 SteamLoginService.LoginAsync Steam auth token
6 RustCompanionClient.RegisterAsync device subscribed to pairing pushes
7 CredentialsStore.Save rustplus.config.json
8 PairingListener ServerPairing (ip/port/playerId/playerToken)

Steps 1–7 run once. Step 8 happens every time you pair a new server in game.

Steam login requires Chrome/Chromium

The Facepunch login page hands the auth token to its host via ReactNativeWebView.postMessage, which can only be intercepted in a Chromium browser driven through the Chrome DevTools Protocol (CDP). SteamLoginService injects a shim via Page.addScriptToEvaluateOnNewDocument — the same mechanism Puppeteer and Playwright use — so the shim runs before any page script and sidesteps the cross-origin WindowProxy restrictions that blocked older techniques. Firefox and Safari will not work.

Browser discovery order

SteamLoginService.FindChrome() and SteamLoginService.ResolveChromeLaunch() locate the browser in this exact order (source: src/RustPlusApi.Fcm.Registration/Steps/SteamLoginService.cs):

  1. CHROME_PATH env var — if set and the path exists as a file, it is used immediately, bypassing all other discovery.
  2. Native binary — Windows (checked via RuntimeInformation.IsOSPlatform): looks for the following paths in order:
    • C:\Program Files\Google\Chrome\Application\chrome.exe
    • C:\Program Files (x86)\Google\Chrome\Application\chrome.exe
    • C:\Program Files (x86)\Microsoft\Edge\Application\msedge.exe
  3. Native binary — macOS: checks in order:
    • /Applications/Google Chrome.app/Contents/MacOS/Google Chrome
    • /Applications/Chromium.app/Contents/MacOS/Chromium
  4. Native binary — Linux (and other platforms): walks PATH for the first match among these names, in order: google-chrome, google-chrome-stable, chromium, chromium-browser, microsoft-edge.
  5. Flatpak — if no native binary was found and flatpak is on PATH, checks for installed Flatpak apps in this order: com.google.Chrome, org.chromium.Chromium, com.github.Eloston.UngoogledChromium. Presence is determined by checking whether the app directory exists under /var/lib/flatpak/app/<id> (system-wide) or ~/.local/share/flatpak/app/<id> (user install). When a Flatpak app is found, Chrome is launched as flatpak run --filesystem=<workDir> <appId> with a temporary profile directory passed in so Chrome can write its data.

If no browser is found at all, LaunchChrome throws InvalidOperationException with a message that includes instructions to install Chrome/Chromium or set CHROME_PATH.

Upstream fragility

Every network step depends on live Google, Expo and Facepunch services, whose endpoints and constants drift when those apps change. The flow is ported from rustplus.js / @liamcottle/push-receiver; if registration breaks, re-check RegistrationConstants against those upstream sources. The offline test suite covers the deterministic parts; the live flow is validated by running the RustPlus.Register.ConsoleApp sample end to end.

Loading credentials back

var credentials = CredentialsStore.Load("rustplus.config.json");
var listener = new RustPlusFcm(credentials);

The legacy rustplus.js rustplus.config.json format is also accepted by the FCM sample's loader.

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