Novato com Spring Security (Request method 'POST' not supported)

[Dklein]

Galera, boa noite!

Estou tentando fazer uma aplicação com Spring Security, JSF e Hibernate. Estou tendo diversas dificuldades e empaquei em uma delas: quando tento fazer meu login recebo a mensagem HTTP method POST is not supported by this URL. Procurei por aí e vi que é um problema comum, mas não consigo achar qual a causa exata no meu caso e muito menos entender como fazer funcionar. Vocês me ajudariam?

Este aqui é meu applicationContext.xml:

<?xml version="1.0" encoding="UTF-8"?>
 
<b:beans xmlns="http://www.springframework.org/schema/security"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:b="http://www.springframework.org/schema/beans"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
                        http://www.springframework.org/schema/beans/spring-beans.xsd
                        http://www.springframework.org/schema/security
                        http://www.springframework.org/schema/security/spring-security-4.1.xsd">
 
    <http auto-config="false" >
        <form-login login-page="/login.xhtml"
            authentication-failure-url="/login.xhtml?error=true" />
        <logout logout-success-url="/login.xhtml" />
 
        <intercept-url pattern="/index.xhtml" access="ROLE_USER" />
    </http>
 
    <authentication-manager>
        <authentication-provider>
            <jdbc-user-service data-source-ref="dataSource"
                users-by-username-query="SELECT username, password, enable FROM User WHERE username=?"
                authorities-by-username-query="SELECT User_username AS username, Auth_authority AS authority FROM User_Auth WHERE User_username=?" />
        </authentication-provider>
    </authentication-manager>
 
    <b:bean id="dataSource"
        class="org.springframework.jdbc.datasource.DriverManagerDataSource">
        <b:property name="url"
            value="jdbc:mysql://localhost:3306/caixaeestoque" />
        <b:property name="driverClassName" value="com.mysql.jdbc.Driver" />
        <b:property name="username" value="root" />
        <b:property name="password" value="" />
    </b:bean>
</b:beans>

Este é meu web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns="http://xmlns.jcp.org/xml/ns/javaee"
	xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
	version="3.1">

	<display-name>caixaeestoque-web</display-name>

	<welcome-file-list>
        <welcome-file>index.xhtml</welcome-file>
    </welcome-file-list>

	<!-- JSF mapping -->
	<servlet>
		<servlet-name>Faces Servlet</servlet-name>
		<servlet-class>javax.faces.webapp.FacesServlet</servlet-class>
		<load-on-startup>1</load-on-startup>
	</servlet>
	<servlet-mapping>
		<servlet-name>Faces Servlet</servlet-name>
		<url-pattern>*.xhtml</url-pattern>
        <url-pattern>*.jsf</url-pattern>
        <url-pattern>/faces/*</url-pattern>
	</servlet-mapping>
	
	
	<context-param>
        <description>State saving method: 'client' or 'server'.</description>
        <param-name>javax.faces.STATE_SAVING_METHOD</param-name>
        <param-value>server</param-value>
    </context-param>
    <context-param>
        <param-name>javax.servlet.jsp.jstl.fmt.localizationContext</param-name>
        <param-value>resources.application</param-value>
    </context-param>
    <filter>
        <filter-name>springSecurityFilterChain</filter-name>
        <filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>springSecurityFilterChain</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>
    <listener>
        <listener-class>com.sun.faces.config.ConfigureListener</listener-class>
    </listener>
    <listener>
        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
    </listener>

</web-app>

Tenho uma entidade para os usuários.

@Entity
@Table(name = "USER")
public class User implements Serializable {
    private static final long serialVersionUID = 1L;
 
    @Id
    @Column(name = "username", length = 40)
    private String username;
    @Column(name = "password", length = 40)
    private String password;
    @Column(name = "enable", columnDefinition = "BOOLEAN")
    private boolean enable;
    @ManyToMany
    @JoinTable(name = "USER_AUTH", joinColumns = @JoinColumn(name = "USER_Username"), inverseJoinColumns = @JoinColumn(name = "AUTH_authority"))
    private List<Authority> authorities;

Esta outra entidade são para os roles:

@Entity
@Table(name = "AUTHORITY")
public class Authority implements Serializable {
    private static final long serialVersionUID = 1L;
 
    @Id
    private String name;

E, por fim, esta é minha página de login.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml"
	xmlns:ui="http://java.sun.com/jsf/facelets"
	xmlns:h="http://java.sun.com/jsf/html"
	xmlns:f="http://java.sun.com/jsf/core"
	xmlns:p="http://primefaces.org/ui">
<h:head>
	<f:view locale="#{localeControllerMB.locale}" contentType="text/html; charset=UTF-8" encoding="UTF-8" />
	<f:loadBundle basename="messages" var="msg" />
	
</h:head>
<h:body>
	<center>
		<h:outputText value="Usuário e/  ou senha inválidos!"
			rendered="#{param.error}"
			style="color:darkred; font-size: 14px; padding-bottom: 10px;" />

		<form action="j_spring_security_check" method="post" >
			<h:panelGrid columns="2" cellpadding="3" style="font-weight: bold;">
			
				<h:outputLabel for="j_username" value="* Usuário:" />
				<h:inputText id="j_username" size="15" />

				<h:outputLabel for="j_password" value="* Senha:" />
				<h:inputSecret id="j_password" size="15" />

				<input type="hidden" name="${_csrf.parameterName}" value="${_csrf.token}"/>
			</h:panelGrid>
			<h:commandButton value="Entrar" />
		</form>
	</center>
</h:body>
</html>

Alguma idéia?