How is AuthStack different from Auth0, Clerk, or Stytch?

AuthStack uses usage-based pricing (per active user per month) instead of per-seat tiers. The first 1,000 monthly active users are free, then you pay only for what you actually use. The OAuth 2.0, JWT, SSO, and passkey feature set matches the major incumbents.

Does AuthStack support passwordless authentication and WebAuthn passkeys?

Yes. AuthStack supports WebAuthn / FIDO2 passkeys (Touch ID, Face ID, Windows Hello, hardware keys) as both a primary sign-in method and a second factor, plus TOTP-based 2FA, magic links, and OAuth-only signup.

Which platforms have first-class SDKs?

Flutter (Dart) via the voo_authstack_client package and .NET (C#) via the AuthStack.Client NuGet package. Both ship typed clients for OAuth code-grant, JWT validation, refresh, and the end-user account surface (profile, sessions, MFA, passkeys).

Can I use my own SMTP and email templates?

Yes. Each organization can configure its own SMTP server or SendGrid account, and override the verification and password-reset email templates per-app with branded HTML and variable substitution.

What's the pricing model?

1,000 monthly active users (MAU) and 10,000 API calls are free every month. Beyond that, $0.005 per MAU and $0.10 per 1,000 API calls. There are no seat fees, no minimum commitments, and no charge for additional OAuth client apps within the same organization.

Is AuthStack an OAuth 2.0 provider or an OAuth 2.0 client?

Both. AuthStack acts as an OpenID Connect / OAuth 2.0 authorization server for your end-users (you become a provider for your apps), and it can broker upstream OAuth providers (Google, GitHub, Microsoft, Apple, Discord) so your users can sign in with their existing accounts.

Flutter SDK

Flutter authentication that just drops in

voo_authstack_client is the typed Dart client for AuthStack — OAuth 2.0, JWT refresh, SSO providers, WebAuthn passkeys, and TOTP MFA in a single package. Works on Flutter web, iOS, Android, macOS, Windows, and Linux. Open-source, MIT-licensed, on pub.dev.

Quick start Integration guide

# 1. Add the package
flutter pub add voo_authstack_client

# 2. Initialize once at app boot
final auth = VooAuthstackService(
  config: VooAuthstackConfig(
    baseUrl: 'https://api.authstack.voostack.com',
  ),
);
await auth.initialize();

# 3. Sign in (email + password)
final result = await auth.loginWithEmail(
  email: 'user@example.com',
  password: '••••••••',
);

# 4. Or hand off to hosted OAuth/passkey UI
final authUrl = await auth.getProviderAuthUrl(
  provider: OAuthProvider.github,
  redirectUri: 'https://yourapp.com/callback',
);
// → launch authUrl in a webview, exchange the code, you're in.

Why teams pick AuthStack over Firebase Auth or Auth0 for Flutter

Typed Dart, not bridged JS

voo_authstack_client is a first-party Dart package. No platform channels, no JS interop, no FlutterFire setup. Same code on Flutter web and native.

Usage-based, not per-MAU-tier

1,000 monthly active users free, then $0.005/MAU. Auth0's Flutter SDK starts at $35/month and locks WebAuthn behind their B2C plan. We don't tier features.

Passkeys + MFA out of the box

WebAuthn / FIDO2 passkeys and TOTP 2FA are in the free tier. Touch ID, Face ID, Windows Hello, and hardware keys work the same way on every Flutter platform.

Hosted auth pages, branded per app

Skip building your own forms. We host the sign-in / signup / password-reset pages with your logo, primary color, and email templates — your end-users never see "AuthStack".

OAuth providers without OAuth setup

Google, GitHub, Microsoft, Apple, Discord — we manage the OAuth app registrations and credentials. You toggle providers in the dashboard, they appear in the SDK.

Open source SDK

Source on GitHub. MIT-licensed. Audit it, fork it, replace it — your call. The backend is the only thing we run for you.

Get started with the Flutter SDK

The integration guide walks through the full OAuth code-grant flow, token refresh, passkey enrollment, and the end-user account surface (profile, sessions, MFA).

Read the guide pub.dev