Ory Kratos

Ory Kratos is an API-first identity and user management system for cloud-native applications. It centralizes self-service login, registration, account verification, password/account recovery, multi-factor authentication, and profile management into a set of HTTP APIs, so applications consume these flows instead of reimplementing them from scratch.

It's deliberately headless - Kratos exposes browser-based and native-app authentication flows over APIs, but doesn't ship its own login UI, so it works with any frontend framework. It's built to scale to large numbers of identities and devices, and integrates with the wider Ory stack (Ory Hydra for OAuth2/OpenID Connect, Ory Keto for access control) when those capabilities are needed. It can be self-hosted or run on the managed Ory Network.

Kratos is a fit for teams that want to remove identity logic from their application code entirely and consume it as an API, while keeping full control over their own login UI rather than adopting a pre-built one.