KMP Multi Auth

A Kotlin Multiplatform authentication library for Android & iOS — built on Supabase Auth.

One dependency. Four auth methods. Zero boilerplate.

Features

• Google Sign-In — Native Credential Manager (Android) + OAuth (iOS)
• Apple Sign-In — Native Sign in with Apple via Supabase ComposeAuth
• Magic Link (Email OTP) — Passwordless email authentication via Supabase
• Anonymous / Guest — Let users try your app without signing up
• Kotlin Multiplatform — Single codebase for Android + iOS
• Compose Multiplatform UI — Ready-made screens and individual buttons
• Fully Customizable — Colors, strings, branding, auth methods, i18n
• 3-Level API — Use full screens, individual buttons, or headless auth
• Dark Mode — Automatic light/dark theme support via MaterialTheme
• Reactive State — Flow<AuthState> for observing session changes

Installation

Add the dependency in your module's build.gradle.kts:

// KMP (commonMain)
implementation("io.github.xemb0:auth:1.0.0")

// Android-only
implementation("io.github.xemb0:auth-android:1.0.0")

That's it — resolves from Maven Central, no extra repositories needed.

Quick Start

1. Initialize

AuthConfig.initialize(
    supabaseUrl = "https://your-project.supabase.co",
    supabaseAnonKey = "your-anon-key",
    googleWebClientId = "your-google-client-id",
    deepLinkScheme = "com.your.app",
    appName = "MyApp",
    appTagline = "Welcome back!",
    enabledMethods = setOf(
        AuthMethod.GOOGLE,
        AuthMethod.APPLE,
        AuthMethod.EMAIL,       // Magic Link
        AuthMethod.ANONYMOUS    // Optional guest mode
    )
)

2. Show the Auth Screen

AuthScreen(
    supabaseClient = supabaseClient,
    googleSignInService = googleSignInService,
    authManager = authManager,
    onAuthenticated = { /* navigate to home */ },
    onEmailSignIn = { /* navigate to magic link flow */ }
)

That's it. You get a fully styled login screen with all enabled providers.

3-Level API

Level 1: Full Screens

Drop-in screens that handle the entire auth flow.

// Auth gate — auto-routes based on session state
AuthGate(
    authManager = authManager,
    authContent = { AuthScreen(...) },
    authenticatedContent = { HomeScreen() }
)

Screens included:

Screen	Description
AuthScreen	Full login screen with all configured providers
AuthGate	Session-aware gate (loading → login or content)
MagicLinkEmailScreen	Email input for magic link / OTP
MagicLinkOtpScreen	"Check your email" confirmation screen

Level 2: Individual Buttons

Use standalone buttons anywhere in your UI.

GoogleSignInButton(
    supabaseClient = supabaseClient,
    googleSignInService = googleSignInService,
    onResult = { result ->
        when (result) {
            is AuthResult.Success -> { /* logged in */ }
            is AuthResult.Cancelled -> { /* user cancelled */ }
            is AuthResult.Error -> { /* show error */ }
        }
    }
)

AppleSignInButton(
    supabaseClient = supabaseClient,
    onResult = { /* handle result */ }
)

EmailSignInButton(
    onClick = { /* navigate to magic link flow */ }
)

AnonymousSignInButton(
    authManager = authManager,
    onResult = { /* handle result */ }
)

All buttons are individually customizable (text, shape, height, colors).

Level 3: Headless

Use AuthManager directly — no UI, full control.

val authManager: AuthManager = SupabaseAuthManager(supabaseClient)

// Anonymous sign-in
val userId = authManager.signInAnonymously()

// Magic link
authManager.sendMagicLink("user@example.com")

// Check session
val isLoggedIn = authManager.isAuthenticated()
val user: AuthUser? = authManager.getCurrentUser()
val token: String? = authManager.getAccessToken()

// Observe auth state reactively
authManager.observeAuthState().collect { state ->
    when (state) {
        is AuthState.Loading -> { /* restoring session */ }
        is AuthState.Authenticated -> { /* user.id = state.userId */ }
        is AuthState.Unauthenticated -> { /* show login */ }
    }
}

// Sign out
authManager.signOut()

Customization

Branding

AuthConfig.initialize(
    // ...
    appName = "MyApp",
    appTagline = "Your awesome tagline",
    appLogo = { Image(painterResource(R.drawable.logo), "Logo") },  // or null for text
    appNameColor = Color(0xFF6C63FF),
    primaryColor = Color(0xFF6C63FF),    // null = use MaterialTheme
    accentColor = Color(0xFFFF6584),
)

Enable/Disable Auth Methods

// Only Google + Email (Magic Link)
enabledMethods = setOf(AuthMethod.GOOGLE, AuthMethod.EMAIL)

// Only Apple
enabledMethods = setOf(AuthMethod.APPLE)

// All four
enabledMethods = setOf(AuthMethod.GOOGLE, AuthMethod.APPLE, AuthMethod.EMAIL, AuthMethod.ANONYMOUS)

Custom Strings (i18n)

AuthConfig.initialize(
    // ...
    strings = object : AuthStrings() {
        override val welcome = "Bienvenido"
        override val continueWithGoogle = "Continuar con Google"
        override val signInWithApple = "Iniciar sesion con Apple"
        override val continueWithEmail = "Continuar con Email"
        override val continueAsGuest = "Continuar como invitado"
        override val orDivider = "o"
        override val termsOfService = "Al continuar, aceptas nuestros Terminos de Servicio"
    }
)

Content Slots

AuthScreen(
    // ...
    headerContent = {
        Text("Special offer: 50% off!", style = MaterialTheme.typography.bodyLarge)
    },
    footerContent = {
        TextButton(onClick = { /* privacy policy */ }) {
            Text("Privacy Policy")
        }
    }
)

Auth Callbacks (Analytics)

val callbacks = object : AuthCallbacks {
    override suspend fun onLoginSuccess(userId: String, method: String) {
        analytics.log("login_success", mapOf("method" to method))
    }
    override suspend fun onLoginError(method: String, error: String) {
        analytics.log("login_error", mapOf("method" to method, "error" to error))
    }
    override suspend fun onSignOut() {
        analytics.log("sign_out")
    }
}

Koin Integration

The library ships with Koin modules for dependency injection:

// In your app's Koin setup
startKoin {
    modules(
        authModule,           // provides AuthManager
        authPlatformModule,   // provides GoogleSignInService (platform-specific)
        // your app modules...
    )
}

Deep Link Setup

Android

Add to your AndroidManifest.xml:

<intent-filter>
    <action android:name="android.intent.action.VIEW" />
    <category android:name="android.intent.category.DEFAULT" />
    <category android:name="android.intent.category.BROWSABLE" />
    <data android:scheme="com.your.app" android:host="login-callback" />
</intent-filter>

Handle in your Activity:

override fun onNewIntent(intent: Intent) {
    super.onNewIntent(intent)
    handleAuthDeepLink(intent)
}

iOS

Add URL scheme in Info.plist and handle in AppDelegate:

func application(_ app: UIApplication, open url: URL, options: ...) -> Bool {
    handleAuthDeepLink(url: url)
    return true
}

Requirements

	Version
Kotlin	2.3+
Compose Multiplatform	1.10+
Supabase BOM	3.3+
Android minSdk	26
iOS	arm64, simulatorArm64

License

MIT License

Copyright (c) 2025 Xemb0

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.