Clerk

Clerk is an authentication service that ships prebuilt user interface components alongside the underlying session infrastructure. The pitch is that sign-in, sign-up, profile management, and organization switching should not be a multi-week build for every application. The integration is a set of components rather than a form the developer assembles. A React application mounts a provider, and the sign-in and user-profile surfaces render with the application's styling. Underneath, Clerk manages sessions, password hashing, multi-factor flows, and social providers. Beyond basic authentication, Clerk models organizations: a user can belong to several organizations with different roles, and the session carries the active organization so application code can authorize against it. The service publishes documentation, a changelog, and a status page, and the SDKs are open source even though the service itself is not.