Auth0 essentially provides authentication and authorization services to various applications. It is also used to prevent DDoS attacks, federate enterprise directory services, implement user management solutions, and as an identity solution provider.

Auth0 provides two APIs for developers, the Authentication API, and the Management API. Authentication API exposes identity functionality for Auth0 and supported identity protocols, including OpenID Connect, OAuth, and SAML. One should use this API through one of the Auth0 SDKs, such as Auth0.js, or a library like Lock. To build your authentication UI manually, you will need to call the Authentication API directly. The Management API allows managing Auth0 accounts programmatically, so you can automate the configuration of your environment. Tasks such as registering your applications and APIs with Auth0, setting up authentication connections for users, managing users, etc. can be performed programmatically using this API.

While SSO and OAuth have some similarities, they are not the same. SSO (Single Sign-On) is when a user uses the same credentials to access multiple domains. However, OAuth is an Authorization protocol that allows a user to selectively grant access to their assets without actually sharing the initial, related, single login credentials.