Authy

Develop, secure, and manage user identities of your product - for both authentication and authorization. Free for up to 5,000 MAUs with open-source self-hosted option available.

Keycloak Open Source Identity and Access Management. Free realm up to 1000 users, up to 10 SSO connections, leveraging Phase Two's Keycloak enhanced container which includes the Organization extension.

Two-factor authentication (2FA) for website or app. Free for ten users, all authentication methods, unlimited, integrations, hardware tokens.

Highly customizable AuthN flows, has both a no-code and API/SDK approach, Free 7,500 active users/month, 50 tenants (up to 5 SAML/SSO tenants).

User management, authentication, 2FA/MFA, prebuilt UI components for sign-in, sign-up, user profiles, and more. Free plan includes unlimited applications, 50,000 MRU limit per app, 3 dashboard seats, and more.

Bring Passwordless, OTPs, 2FA, SSO to your apps in minutes. All Front-end included. Free up to 5000 MAUs.

Hosted SSO. The free plan includes 25,000 MAUs, unlimited Social Connections, a custom domain, and more.

Open-source API key management and rate-limiting platform. Free for up to 100,000 requests per month and 100 active API keys, with full access to key creation, revocation, and rate-limiting capabilities.