Form Login

Spring Security provides support for username and password being provided through an HTML form. This section provides details on how form based authentication works within Spring Security.

This section examines how form-based login works within Spring Security. First, we see how the user is redirected to the login form:

Figure 1. Redirecting to the Login Page

The preceding figure builds off our SecurityFilterChain diagram.

number 1 First, a user makes an unauthenticated request to the resource (/private) for which it is not authorized.

number 2 Spring Security’s AuthorizationFilter indicates that the unauthenticated request is Denied by throwing an AccessDeniedException.

number 3 Since the user is not authenticated, ExceptionTranslationFilter initiates Start Authentication and sends a redirect to the login page with the configured AuthenticationEntryPoint. In most cases, the AuthenticationEntryPoint is an instance of LoginUrlAuthenticationEntryPoint.

number 4 The browser requests the login page to which it was redirected.

number 5 Something within the application, must render the login page.

When the username and password are submitted, the UsernamePasswordAuthenticationFilter creates a UsernamePasswordAuthenticationToken which is a type of Authentication, by extracting the username and password from the HttpServletRequest instance. The UsernamePasswordAuthenticationFilter extends AbstractAuthenticationProcessingFilter, so the following diagram should look pretty similar:

Figure 2. Authenticating Username and Password

The figure builds off our SecurityFilterChain diagram.

number 1 When the user submits their username and password, the UsernamePasswordAuthenticationFilter creates a UsernamePasswordAuthenticationToken, which is a type of Authentication, by extracting the username and password from the HttpServletRequest instance.

number 2 Next, the UsernamePasswordAuthenticationToken is passed into the AuthenticationManager instance to be authenticated. The details of what AuthenticationManager looks like depend on how the user information is stored.

number 3 If authentication fails, then Failure.

The SecurityContextHolder is cleared out.
RememberMeServices.loginFail is invoked. If remember me is not configured, this is a no-op. See the RememberMeServices interface in the Javadoc.
AuthenticationFailureHandler is invoked. See the AuthenticationFailureHandler class in the Javadoc

number 4 If authentication is successful, then Success.

SessionAuthenticationStrategy is notified of a new login. See the SessionAuthenticationStrategy interface in the Javadoc.
The Authentication is set on the SecurityContextHolder. See the SecurityContextPersistenceFilter class in the Javadoc.
RememberMeServices.loginSuccess is invoked. If remember me is not configured, this is a no-op. See the RememberMeServices interface in the Javadoc.
ApplicationEventPublisher publishes an InteractiveAuthenticationSuccessEvent.
The AuthenticationSuccessHandler is invoked. Typically, this is a SimpleUrlAuthenticationSuccessHandler, which redirects to a request saved by ExceptionTranslationFilter when we redirect to the login page.

By default, Spring Security form login is enabled. However, as soon as any servlet-based configuration is provided, form based login must be explicitly provided. The following example shows a minimal, explicit Java configuration:

Form Login

Java
XML
Kotlin

public SecurityFilterChain filterChain(HttpSecurity http) {
	http
		.formLogin(withDefaults());
	// ...
}

<http>
	<!-- ... -->
	<form-login />
</http>

open fun filterChain(http: HttpSecurity): SecurityFilterChain {
	http {
		formLogin { }
	}
	// ...
}

In the preceding configuration, Spring Security renders a default login page. Most production applications require a custom login form.

The following configuration demonstrates how to provide a custom login form.

Custom Login Form Configuration

Java
XML
Kotlin

public SecurityFilterChain filterChain(HttpSecurity http) {
	http
		.formLogin(form -> form
			.loginPage("/login")
			.permitAll()
		);
	// ...
}

<http>
	<!-- ... -->
	<intercept-url pattern="/login" access="permitAll" />
	<form-login login-page="/login" />
</http>

open fun filterChain(http: HttpSecurity): SecurityFilterChain {
	http {
		formLogin {
			loginPage = "/login"
			permitAll()
		}
	}
	// ...
}

When the login page is specified in the Spring Security configuration, you are responsible for rendering the page. The following Thymeleaf template produces an HTML login form that complies with a login page of /login.:

<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml" xmlns:th="https://www.thymeleaf.org">
	<head>
		<title>Please Log In</title>
	</head>
	<body>
		<h1>Please Log In</h1>
		<div th:if="${param.error}">
			Invalid username and password.</div>
		<div th:if="${param.logout}">
			You have been logged out.</div>
		<form th:action="@{/login}" method="post">
			<div>
			<input type="text" name="username" placeholder="Username"/>
			</div>
			<div>
			<input type="password" name="password" placeholder="Password"/>
			</div>
			<input type="submit" value="Log in" />
		</form>
	</body>
</html>

There are a few key points about the default HTML form:

The form should perform a post to /login.
The form needs to include a CSRF Token, which is automatically included by Thymeleaf.
The form should specify the username in a parameter named username.
The form should specify the password in a parameter named password.
If the HTTP parameter named error is found, it indicates the user failed to provide a valid username or password.
If the HTTP parameter named logout is found, it indicates the user has logged out successfully.

Many users do not need much more than to customize the login page. However, if needed, you can customize everything shown earlier with additional configuration.

If you use Spring MVC, you need a controller that maps GET /login to the login template we created. The following example shows a minimal LoginController:

LoginController

Java
Kotlin

@Controller
class LoginController {
	@GetMapping("/login")
	String login() {
		return "login";
	}
}

@Controller
class LoginController {
    @GetMapping("/login")
    fun login(): String {
        return "login"
    }
}