[[authentication]]
= Authentication

Spring Security provides comprehensive support for https://en.wikipedia.org/wiki/Authentication[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 xref:servlet/authentication/index.adoc[Servlet] and xref:reactive/authentication/index.adoc[WebFlux] for details on what is supported for each stack.
