[[servlet-authentication-basic]]
= Basic Authentication

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

Let's take a look at 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
image::{figures}/basicauthenticationentrypoint.png[]

The figure builds off our <<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 <<servlet-authorization-filtersecurityinterceptor,`FilterSecurityInterceptor`>> indicates that the unauthenticated request is __Denied__ by throwing an `AccessDeniedException`.

image:{icondir}/number_3.png[] Since the user is not authenticated, <<servlet-exceptiontranslationfilter,`ExceptionTranslationFilter`>> initiates __Start Authentication__.
The configured <<servlet-authentication-authenticationentrypoint,`AuthenticationEntryPoint`>> is an instance of {security-api-url}org/springframework/security/web/authentication/www/BasicAuthenticationEntryPoint.html[`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.

When a client receives the WWW-Authenticate header it knows it should retry with a username and password.
Below is the flow for the username and password being processed.

.Authenticating Username and Password
image::{figures}/basicauthenticationfilter.png[]

The figure builds off our <<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 <<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` look like depend on how the <<servlet-authentication-unpwd-storage,user information is stored>>.

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

* The <<servlet-authentication-securitycontextholder>> is cleared out.
* `RememberMeServices.loginFail` is invoked.
If remember me is not configured, this is a no-op.
// FIXME: link to rememberme
* `AuthenticationEntryPoint` is invoked to trigger the WWW-Authenticate to be sent again.

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

* The <<servlet-authentication-authentication>> is set on the <<servlet-authentication-securitycontextholder>>.
* `RememberMeServices.loginSuccess` is invoked.
If remember me is not configured, this is a no-op.
// FIXME: link to rememberme
* The `BasicAuthenticationFilter` invokes `FilterChain.doFilter(request,response)` to continue with the rest of the application logic.

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

A minimal, explicit configuration can be found below:

.Explicit HTTP Basic Configuration
====
[source,java,role="primary"]
.Java
----
protected void configure(HttpSecurity http) {
	http
		// ...
		.httpBasic(withDefaults());
}
----

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

[source,kotlin,role="secondary"]
.Kotlin
----
fun configure(http: HttpSecurity) {
	http {
		// ...
		httpBasic { }
	}
}
----
====
