Auth

Auth0

A managed authentication and authorization service: sign-in, SSO, MFA and API access with no identity server of your own.

Official site

What it is

Auth0 is a cloud identity provider you connect through SDKs for React, Next.js, mobile and server platforms. It has a ready login page (Universal Login), social providers, MFA and passkeys.

The service is based on OAuth 2.0 and OIDC. It lets you configure rules and Actions on login events, manage roles and connect enterprise IdPs (SAML, Entra ID).

Okta acquired the company in 2021. Pricing is per active user: convenient at the start, but cost grows quickly with scale.

Use it when

  • You need ready sign-in fast, without hosting a server.
  • B2B SaaS with enterprise SSO for customers.
  • The team does not want to run identity security itself.

Avoid it when

  • A very large number of users with low revenue per user: the cost can be too high.
  • A requirement to keep all identity data on your own infrastructure: Keycloak.

Key concepts

Universal Login
A hosted login page that you only style.
Tenant
Your account space in Auth0 with apps and users.
Actions
Server code that runs on login or signup events.
Connections
User sources: database, social, SAML.

Example

A login button with the Auth0 React SDK.

Interview questions

  1. 1. Why not write authentication yourself?

    Safe password storage, MFA, resets, brute-force protection and compliance are hard to get right. A managed provider takes that on.

  2. 2. What are Auth0 Actions?

    Small Node.js functions that run on events such as post-login. They add claims to tokens or block suspicious logins.

  3. 3. What are the vendor lock-in risks?

    Users, password hashes and Actions logic are tied to the provider. Export is possible, but migration needs planning.

Related technologies

Logos belong to their owners and are used for identification only. Icons: Simple Icons (CC0), Devicon (MIT).

Explore the platform