[[servlet-authentication]]
= Authentication

Spring Security provides comprehensive support for <<authentication>>.
This section discusses:

[[servlet-authentication-architecture]]
*Architecture Components*

This section describes the main architectural components of Spring Security's used in Servlet authentication.
If you need concrete flows that explain how these pieces fit together, look at the <<servlet-authentication-mechanisms,Authentication Mechanism>> specific sections.

* <<servlet-authentication-securitycontextholder>> - the `SecurityContextHolder` is where Spring Security stores the details of who is <<authentication,authenticated>>.
* <<servlet-authentication-securitycontext>> - is obtained from the `SecurityContextHolder` and contains the `Authentication` of the currently authenticated user.
* <<servlet-authentication-authentication>> - can be the input to `AuthenticationManager` to provide the credentials a user has provided to authenticate or the current user from the `SecurityContext`.
* <<servlet-authentication-granted-authority>> - an authority that is granted to the principal on the `Authentication` (i.e. roles, scopes, etc.)
* <<servlet-authentication-authenticationmanager>> - the API that defines how Spring Security's Filters perform  <<authentication,authentication>>.
* <<servlet-authentication-providermanager>> - the most common implementation of `AuthenticationManager`.
* <<servlet-authentication-authenticationprovider>> - used by `ProviderManager` to perform a specific type of authentication.
* <<servlet-authentication-authenticationentrypoint>> - used for requesting credentials from a client (i.e. redirecting to a log in page, sending a `WWW-Authenticate` response, etc.)
* <<servlet-authentication-abstractprocessingfilter>> - a base `Filter` used for authentication.
This also gives a good idea of the high level flow of authentication and how pieces work together.

[[servlet-authentication-mechanisms]]
*Authentication Mechanisms*

// FIXME: brief description

* <<servlet-authentication-unpwd,Username and Password>> - how to authenticate with a username/password
* <<oauth2login,OAuth 2.0 Login>> - OAuth 2.0 Log In with OpenID Connect and non-standard OAuth 2.0 Login (i.e. GitHub)
* <<servlet-saml2,SAML 2.0 Login>> - SAML 2.0 Log In
* <<servlet-cas,Central Authentication Server (CAS)>> - Central Authentication Server (CAS) Support
* <<servlet-rememberme, Remember Me>> - how to remember a user past session expiration
* <<servlet-jaas, JAAS Authentication>> - authenticate with JAAS
* <<servlet-openid,OpenID>> - OpenID Authentication (not to be confused with OpenID Connect)
* <<servlet-preauth>> - authenticate with an external mechanism such as https://www.siteminder.com/[SiteMinder] or Java EE security but still use Spring Security for authorization and protection against common exploits.
* <<servlet-x509,X509 Authentication>> - X509 Authentication

// FIXME: Add other mechanisms

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include::rememberme.adoc[]

include::openid.adoc[]

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include::preauth.adoc[]

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include::cas.adoc[]

include::x509.adoc[]

include::runas.adoc[]

include::logout.adoc[]

include::events.adoc[]