[[servlet-authentication-basic]]
= Basic Authentication
:figures: servlet/authentication/unpwd

This section provides details on how Spring Security provides support for https://tools.ietf.org/html/rfc7617[Basic HTTP Authentication] for servlet-based applications.
// FIXME: describe authenticationentrypoint, authenticationfailurehandler, authenticationsuccesshandler

This section describes how HTTP Basic Authentication works within Spring Security.
First, we see the https://tools.ietf.org/html/rfc7235#section-4.1[WWW-Authenticate] header is sent back to an unauthenticated client:

.Sending WWW-Authenticate Header
[.invert-dark]
image::{figures}/basicauthenticationentrypoint.png[]

The preceding figure builds off our xref:servlet/architecture.adoc#servlet-securityfilterchain[`SecurityFilterChain`] diagram.

image:{icondir}/number_1.png[] First, a user makes an unauthenticated request to the resource `/private` for which it is not authorized.

image:{icondir}/number_2.png[] Spring Security's xref:servlet/authorization/authorize-http-requests.adoc[`AuthorizationFilter`] indicates that the unauthenticated request is __Denied__ by throwing an `AccessDeniedException`.

image:{icondir}/number_3.png[] Since the user is not authenticated, xref:servlet/architecture.adoc#servlet-exceptiontranslationfilter[`ExceptionTranslationFilter`] initiates __Start Authentication__.
The configured xref:servlet/authentication/architecture.adoc#servlet-authentication-authenticationentrypoint[`AuthenticationEntryPoint`] is an instance of javadoc:org.springframework.security.web.authentication.www.BasicAuthenticationEntryPoint[], which sends a WWW-Authenticate header.
The `RequestCache` is typically a `NullRequestCache` that does not save the request since the client is capable of replaying the requests it originally requested.

[NOTE]
====
The default HTTP Basic Auth Provider will suppress both Response body and `WWW-Authenticate` header in the 401 response when the request was made with a `X-Requested-With: XMLHttpRequest` header.
This allows frontends to implement their own authentication code, instead of triggering the browser login dialog.
To override, implement your own javadoc:org.springframework.security.web.authentication.www.BasicAuthenticationEntryPoint[].
====

When a client receives the `WWW-Authenticate` header, it knows it should retry with a username and password.
The following image shows the flow for the username and password being processed:

[[servlet-authentication-basicauthenticationfilter]]
.Authenticating Username and Password
[.invert-dark]
image::{figures}/basicauthenticationfilter.png[]

The preceding figure builds off our xref:servlet/architecture.adoc#servlet-securityfilterchain[`SecurityFilterChain`] diagram.


image:{icondir}/number_1.png[] When the user submits their username and password, the `BasicAuthenticationFilter` creates a `UsernamePasswordAuthenticationToken`, which is a type of xref:servlet/authentication/architecture.adoc#servlet-authentication-authentication[`Authentication`] by extracting the username and password from the `HttpServletRequest`.

image:{icondir}/number_2.png[] Next, the `UsernamePasswordAuthenticationToken` is passed into the `AuthenticationManager` to be authenticated.
The details of what `AuthenticationManager` looks like depend on how the xref:servlet/authentication/passwords/index.adoc#servlet-authentication-unpwd[user information is stored].

image:{icondir}/number_3.png[] If authentication fails, then __Failure__.

. The xref:servlet/authentication/architecture.adoc#servlet-authentication-securitycontextholder[SecurityContextHolder] is cleared out.
. `RememberMeServices.loginFail` is invoked.
If remember me is not configured, this is a no-op.
See the javadoc:org.springframework.security.web.authentication.RememberMeServices[] interface in the Javadoc.
. `AuthenticationEntryPoint` is invoked to trigger the WWW-Authenticate to be sent again.
See the javadoc:org.springframework.security.web.AuthenticationEntryPoint[] interface in the Javadoc.

image:{icondir}/number_4.png[] If authentication is successful, then __Success__.

* Any already-authenticated `Authentication` in the xref:servlet/authentication/architecture.adoc#servlet-authentication-securitycontextholder[`SecurityContextHolder`] is loaded and its
authorities are added to the returned xref:servlet/authentication/architecture.adoc#servlet-authentication-authentication[`Authentication`].
. The xref:servlet/authentication/architecture.adoc#servlet-authentication-authentication[Authentication] is set on the xref:servlet/authentication/architecture.adoc#servlet-authentication-securitycontextholder[SecurityContextHolder].
. `RememberMeServices.loginSuccess` is invoked.
If remember me is not configured, this is a no-op.
See the javadoc:org.springframework.security.web.authentication.RememberMeServices[] interface in the Javadoc.
. The `BasicAuthenticationFilter` invokes `FilterChain.doFilter(request,response)` to continue with the rest of the application logic.
See the javadoc:org.springframework.security.web.authentication.www.BasicAuthenticationFilter[] Class in the Javadoc

By default, Spring Security's HTTP Basic Authentication support is enabled.
However, as soon as any servlet based configuration is provided, HTTP Basic must be explicitly provided.

The following example shows a minimal, explicit configuration:

.Explicit HTTP Basic Configuration
[tabs]
======
Java::
+
[source,java,role="primary"]
----
@Bean
public SecurityFilterChain filterChain(HttpSecurity http) {
	http
		// ...
		.httpBasic(withDefaults());
	return http.build();
}
----

XML::
+
[source,xml,role="secondary"]
----
<http>
	<!-- ... -->
	<http-basic />
</http>
----

Kotlin::
+
[source,kotlin,role="secondary"]
----
@Bean
open fun filterChain(http: HttpSecurity): SecurityFilterChain {
	http {
		// ...
		httpBasic { }
	}
	return http.build()
}
----
======
