# Authentication

Spring Security provides comprehensive support for [authentication](https://en.wikipedia.org/wiki/Authentication).
Authentication is how we verify the identity of who is trying to access a particular resource.
A common way to authenticate users is by requiring the user to enter a username and password.
Once authentication is performed we know the identity and can perform authorization.

Spring Security provides built in support for authenticating users.
This section is dedicated to generic authentication support that applies in both Servlet and WebFlux environments.
Refer to the sections on authentication for [Servlet](../../servlet/authentication/index.html#servlet-authentication) and WebFlux for details on what is supported for each stack.