feat: create expo config plugin

CONTRIBUTING.md

@@ -92,6 +92,7 @@ The test suite covers:
 - **JS API tests** (`src/google/__tests__/GoogleSignIn.test.ts`) — the `configure`-then-call contract on the `GoogleSignIn` wrapper, with the native TurboModule mocked.
 - **Error tests** (`src/google/__tests__/errors.test.ts`) — `GoogleSignInError`, the `GoogleSignInErrorCode` enum, and the `isGoogleSignInError` type guard.
 - **Component tests** (`src/google/__tests__/GoogleSignInButton.test.tsx`) — accessibility labels, `onPress` / `disabled` behavior, and theme/shape/text variants, using [React Native Testing Library](https://callstack.github.io/react-native-testing-library/).
+- **Expo config plugin tests** (`plugin/src/__tests__/withSocialAuth.test.ts`) — `Info.plist` URL scheme reversal and `AppDelegate` URL-handler injection, for both Swift and Objective-C fixtures.
 
 `react-native-svg` is mocked via `__mocks__/react-native-svg.js` so the button renders without native bindings during tests.
 
@@ -151,7 +152,8 @@ The `package.json` file contains various scripts for common tasks:
 - `yarn typecheck`: type-check files with TypeScript.
 - `yarn lint`: lint files with [ESLint](https://eslint.org/).
 - `yarn test`: run unit + component tests with [Jest](https://jestjs.io/) and [React Native Testing Library](https://callstack.github.io/react-native-testing-library/).
-- `yarn prepare`: build the library to `lib/` with [react-native-builder-bob](https://github.com/callstack/react-native-builder-bob) (also runs automatically before `npm publish`).
+- `yarn prepare`: build the library to `lib/` with [react-native-builder-bob](https://github.com/callstack/react-native-builder-bob) and compile the Expo config plugin to `plugin/build/` (also runs automatically before `npm publish`).
+- `yarn build:plugin`: compile only the Expo config plugin (faster than `yarn prepare` when iterating on plugin code).
 - `yarn example start`: start the Metro server for the example app.
 - `yarn example android`: run the example app on Android.
 - `yarn example ios`: run the example app on iOS.

README.md

@@ -65,6 +65,8 @@ The Web client ID is what your code references for the ID-token audience; each p
 
 In addition to the Cloud Console step above, the host app needs two iOS-specific changes.
 
+> **Using Expo?** Skip the manual `Info.plist` and `AppDelegate` edits below — [our config plugin](#expo-config-plugin) handles them during `expo prebuild`. Bare React Native CLI users continue with the manual steps in this section.
+
 ### 1. Register the OAuth URL scheme
 
 Google routes the sign-in callback back into your app via a custom URL scheme. Add the reversed iOS Client ID to `Info.plist`:
@@ -124,6 +126,56 @@ GoogleSignIn.configure({
 
 Finally, run `cd ios && pod install` after installing the package.
 
+## Expo config plugin
+
+This package ships an Expo config plugin so you don't have to hand-edit `Info.plist` or `AppDelegate` in Expo projects. **Both React Native CLI and Expo projects are supported** — pick the setup section that matches your project.
+
+> **Heads up:** Expo Go cannot ship third-party native modules. You must use a [development build](https://docs.expo.dev/develop/development-builds/introduction/) (via `expo-dev-client` and EAS Build) or the bare workflow.
+
+### Install
+
+```sh
+npx expo install @thoughtbot/react-native-social-auth react-native-svg
+```
+
+### Add the plugin
+
+In `app.config.ts` (or `app.json`):
+
+```ts
+export default {
+  expo: {
+    // ...
+    plugins: [
+      [
+        '@thoughtbot/react-native-social-auth',
+        {
+          iosClientId: process.env.EXPO_PUBLIC_GOOGLE_IOS_CLIENT_ID,
+        },
+      ],
+    ],
+  },
+};
+```
+
+### Plugin props
+
+| Prop          | Type     | Required for iOS | Description                                                                                                                       |
+| ------------- | -------- | ---------------- | --------------------------------------------------------------------------------------------------------------------------------- |
+| `iosClientId` | `string` | Yes              | Your iOS OAuth Client ID (e.g. `123456-abc.apps.googleusercontent.com`). The plugin reverses it and registers the URL scheme.     |
+
+Omit `iosClientId` if you only target Android — the plugin becomes a no-op on iOS and logs a warning.
+
+### Regenerate native code
+
+```sh
+npx expo prebuild --clean
+```
+
+This runs the plugin, which writes the reversed iOS Client ID into `Info.plist`'s `CFBundleURLSchemes` and adds the `application(_:open:options:)` URL forwarder to `AppDelegate`. Subsequent prebuilds are idempotent — the plugin won't re-inject if its marker is already present.
+
+You still call `GoogleSignIn.configure({ webClientId, iosClientId })` from JS at runtime (the plugin handles the native bits; it doesn't replace `configure()`).
+
 ## Quick start
 
 ```tsx

ROADMAP.md

@@ -64,10 +64,10 @@
 
 ## Phase 6: Expo Support
 
-- [ ] Write an Expo config plugin that handles `Info.plist` URL schemes (iOS) and any Android manifest needs
-- [ ] Test in Expo prebuild / development build workflow
-- [ ] Document Expo managed workflow limitations (if any) and EAS build setup
-- [ ] Add the config plugin to the package's `app.plugin.js` entry
+- [x] Write an Expo config plugin that handles `Info.plist` URL schemes and `AppDelegate` URL forwarding (iOS). Android is a no-op — Credential Manager needs no manifest changes.
+- [x] Test in Expo prebuild / development build workflow (covered by `plugin/src/__tests__/withSocialAuth.test.ts` + the example app)
+- [x] Document Expo managed workflow limitations (Expo Go not supported; dev client / EAS Build required) and the install flow
+- [x] Add the config plugin to the package's `app.plugin.js` entry
 
 ## Phase 7: Documentation
 

app.plugin.js

@@ -0,0 +1 @@
+module.exports = require('./plugin/build/withSocialAuth').default;

eslint.config.mjs

@@ -24,6 +24,6 @@ export default defineConfig([
     },
   },
   {
-    ignores: ['node_modules/', 'lib/'],
+    ignores: ['node_modules/', 'lib/', 'plugin/build/'],
   },
 ]);

example/app.json

@@ -13,17 +13,16 @@
     },
     "ios": {
       "supportsTablet": true,
-      "bundleIdentifier": "thoughtbot.reactnativesocialauth.example",
-      "infoPlist": {
-        "CFBundleURLTypes": [
-          {
-            "CFBundleURLSchemes": [
-              "com.googleusercontent.apps.476683722118-27sdo4g5f7n5egip0r3ig7v3m35q9cql"
-            ]
-          }
-        ]
-      }
+      "bundleIdentifier": "thoughtbot.reactnativesocialauth.example"
     },
+    "plugins": [
+      [
+        "@thoughtbot/react-native-social-auth",
+        {
+          "iosClientId": "476683722118-27sdo4g5f7n5egip0r3ig7v3m35q9cql.apps.googleusercontent.com"
+        }
+      ]
+    ],
     "android": {
       "adaptiveIcon": {
         "backgroundColor": "#E6F4FE",

example/package.json

@@ -13,6 +13,7 @@
   },
   "dependencies": {
     "@expo/metro-runtime": "~55.0.9",
+    "@thoughtbot/react-native-social-auth": "workspace:^",
     "expo": "~55.0.15",
     "expo-status-bar": "~55.0.5",
     "react": "19.2.0",

package.json

@@ -18,6 +18,8 @@
     "android",
     "ios",
     "cpp",
+    "plugin/build",
+    "app.plugin.js",
     "*.podspec",
     "react-native.config.js",
     "!ios/build",
@@ -33,8 +35,9 @@
   ],
   "scripts": {
     "example": "yarn workspace @thoughtbot/react-native-social-auth-example",
-    "clean": "del-cli lib",
-    "prepare": "bob build",
+    "clean": "del-cli lib plugin/build",
+    "prepare": "bob build && yarn build:plugin",
+    "build:plugin": "tsc --project plugin/tsconfig.json",
     "typecheck": "tsc",
     "test": "jest",
     "release": "release-it --only-version",
@@ -68,12 +71,14 @@
     "@eslint/compat": "^2.0.3",
     "@eslint/eslintrc": "^3.3.5",
     "@eslint/js": "^10.0.1",
+    "@expo/config-plugins": "^9",
     "@jest/globals": "^30.0.0",
     "@react-native/babel-preset": "0.85.0",
     "@react-native/eslint-config": "0.85.0",
     "@react-native/jest-preset": "0.85.0",
     "@release-it/conventional-changelog": "^10.0.6",
     "@testing-library/react-native": "^13.3",
+    "@types/node": "^26.0.1",
     "@types/react": "^19.2.0",
     "@types/react-test-renderer": "^19",
     "commitlint": "^20.5.0",
@@ -82,6 +87,7 @@
     "eslint-config-prettier": "^10.1.8",
     "eslint-plugin-ft-flow": "^3.0.11",
     "eslint-plugin-prettier": "^5.5.5",
+    "expo": "^56.0.12",
     "jest": "^30.3.0",
     "lefthook": "^2.1.4",
     "prettier": "^3.8.1",
@@ -95,10 +101,16 @@
     "typescript": "^6.0.2"
   },
   "peerDependencies": {
+    "@expo/config-plugins": ">=9.0.0",
     "react": "*",
     "react-native": "*",
     "react-native-svg": ">=13.0.0"
   },
+  "peerDependenciesMeta": {
+    "@expo/config-plugins": {
+      "optional": true
+    }
+  },
   "workspaces": [
     "example"
   ],

plugin/src/__tests__/withSocialAuth.test.ts

@@ -0,0 +1,98 @@
+import { describe, expect, it } from '@jest/globals';
+import {
+  injectObjCURLHandler,
+  injectSwiftURLHandler,
+  reverseClientId,
+} from '../withSocialAuth';
+
+describe('reverseClientId', () => {
+  it('reverses a valid iOS client ID', () => {
+    expect(reverseClientId('123456-abc.apps.googleusercontent.com')).toBe(
+      'com.googleusercontent.apps.123456-abc'
+    );
+  });
+
+  it('throws on a Web client ID (missing iOS suffix)', () => {
+    expect(() => reverseClientId('123456-xyz.example.com')).toThrow(
+      /must end with "\.apps\.googleusercontent\.com"/
+    );
+  });
+
+  it('throws on an empty string', () => {
+    expect(() => reverseClientId('')).toThrow();
+  });
+});
+
+const SWIFT_FIXTURE = `import Expo
+import ExpoModulesCore
+
+@UIApplicationMain
+public class AppDelegate: ExpoAppDelegate {
+  public override func application(
+    _ application: UIApplication,
+    didFinishLaunchingWithOptions launchOptions: ...
+  ) -> Bool {
+    return super.application(application, didFinishLaunchingWithOptions: launchOptions)
+  }
+}
+`;
+
+describe('injectSwiftURLHandler', () => {
+  it('adds the import and URL handler override', () => {
+    const out = injectSwiftURLHandler(SWIFT_FIXTURE);
+    expect(out).toContain('import react_native_social_auth');
+    expect(out).toContain('GoogleSignIn.handleURL(url)');
+    expect(out).toContain(
+      'public override func application(\n    _ app: UIApplication'
+    );
+  });
+
+  it('places the override inside the AppDelegate class (before the closing brace)', () => {
+    const out = injectSwiftURLHandler(SWIFT_FIXTURE);
+    const handlerIndex = out.indexOf('GoogleSignIn.handleURL');
+    const lastBraceIndex = out.lastIndexOf('}');
+    expect(handlerIndex).toBeLessThan(lastBraceIndex);
+  });
+
+  it('throws if the closing brace cannot be located', () => {
+    expect(() => injectSwiftURLHandler('// no class here')).toThrow(
+      /closing brace/
+    );
+  });
+});
+
+const OBJC_FIXTURE = `#import "AppDelegate.h"
+#import <React/RCTBundleURLProvider.h>
+
+@implementation AppDelegate
+
+- (BOOL)application:(UIApplication *)application
+    didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
+{
+  return [super application:application didFinishLaunchingWithOptions:launchOptions];
+}
+
+@end
+`;
+
+describe('injectObjCURLHandler', () => {
+  it('adds the import and openURL method', () => {
+    const out = injectObjCURLHandler(OBJC_FIXTURE);
+    expect(out).toContain('#import <react_native_social_auth/GoogleSignIn.h>');
+    expect(out).toContain('[GoogleSignIn handleURL:url]');
+    expect(out).toContain(
+      '- (BOOL)application:(UIApplication *)application\n            openURL:(NSURL *)url'
+    );
+  });
+
+  it('places the method before @end', () => {
+    const out = injectObjCURLHandler(OBJC_FIXTURE);
+    const handlerIndex = out.indexOf('[GoogleSignIn handleURL:url]');
+    const endIndex = out.lastIndexOf('@end');
+    expect(handlerIndex).toBeLessThan(endIndex);
+  });
+
+  it('throws if @end is missing', () => {
+    expect(() => injectObjCURLHandler('// no class here')).toThrow(/@end/);
+  });
+});