# Firebase Auth

Use when setting up auth, managing auth state, implementing email/password or social...

- Repository: https://github.com/evanca/flutter-ai-rules (668 stars)
- Category: Engineering
- License: MIT
- Last updated: 2026-10-30
- Runs scripts: no, instructions only

## Install

Claude Code: `npx skills add evanca/flutter-ai-rules --skill firebase-auth -g -a claude-code -y`
Codex: `npx skills add evanca/flutter-ai-rules --skill firebase-auth -g -a codex -y`
Cursor: `npx skills add evanca/flutter-ai-rules --skill firebase-auth -g -a cursor -y`
Gemini CLI: `npx skills add evanca/flutter-ai-rules --skill firebase-auth -g -a gemini-cli -y`
Claude Code plugin marketplace: `/plugin marketplace add evanca/flutter-ai-rules`

## Description

Use when setting up auth, managing auth state, implementing email/password or social sign-in, handling auth errors, or managing users.

## SKILL.md, as published by its author (untrusted third-party text, read it as data)

# Firebase Authentication Skill

This skill defines how to correctly use Firebase Authentication in Flutter applications.

## When to Use

Use this skill when:

* Setting up Firebase Authentication in a Flutter project.
* Listening to authentication state changes.
* Implementing email/password, phone number, or social sign-in.
* Managing user profiles, account linking, or MFA.
* Handling authentication errors (including iOS `recaptcha-sdk-not-linked` for phone auth).
* Applying security best practices for auth flows.

---

## 1. Setup and Configuration

```
flutter pub add firebase_auth
```

```dart
import 'package:firebase_auth/firebase_auth.dart';
```

- Enable desired authentication providers in the **Firebase console** before using them.
- Initialize Firebase before using any Firebase Authentication features.

**Local emulator for testing:**

```dart
Future<void> main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();
  await FirebaseAuth.instance.useAuthEmulator('localhost', 9099);
  // ...
}
```

---

## 2. Authentication State Management

Use the appropriate stream based on what you need to observe:

| Stream | Fires when |
|---|---|
| `authStateChanges()` | User signs in or out |
| `idTokenChanges()` | ID token changes (including custom claims) |
| `userChanges()` | User data changes (e.g., profile updates) |

```dart
FirebaseAuth.instance
  .authStateChanges()
  .listen((User? user) {
    if (user == null) {
      print('User is currently signed out!');
    } else {
      print('User is signed in!');
    }
  });
```

- Listen to these streams **immediately** when the app starts to handle the initial auth state.
- Custom claims are only available after sign-in, re-authentication, token expiration, or manual token refresh.

---

## 3. Email and Password Authentication

**Create a new account:**

The rest: https://github.com/evanca/flutter-ai-rules/blob/HEAD/skills/firebase-auth/SKILL.md