Why is this BeanPostProcessor needed in addition to a UserDetailsService in this Spring 3.0 authentication example?

Question

I'm trying to understand a Spring 3.0 application which contains the following BeanPostProcessor implementation. What is this code needed for? I thought the UserDetailsService was sufficient for getting and setting the User account information.

@Service
public class UserPassAuthFilterBeanPostProcessor implements BeanPostProcessor
{

    /**
     * The username parameter.
     */
    private String usernameParameter;

    /**
     * The password parameter.
     */
    private String passwordParameter;

    @Override
    public final Object postProcessAfterInitialization(final Object bean, final String beanName)
    {
        return bean;
    }

    @Override
    public final Object postProcessBeforeInitialization(final Object bean, final String beanName)
    {
        if (bean instanceof UsernamePasswordAuthenticationFilter)
        {
            final UsernamePasswordAuthenticationFilter filter = (UsernamePasswordAuthenticationFilter) bean;
            filter.setUsernameParameter(getUsernameParameter());
            filter.setPasswordParameter(getPasswordParameter());
        }

        return bean;
    }

    /**
     * Sets the username parameter.
     * 
     * @param usernameParameter
     *         the username parameter
     */
    public final void setUsernameParameter(final String usernameParameter)
    {
        this.usernameParameter = usernameParameter;
    }

    /**
     * Gets the username parameter.
     * 
     * @return the username parameter
     */
    public final String getUsernameParameter()
    {
        return usernameParameter;
    }

    /**
     * Sets the password parameter.
     * 
     * @param passwordParameter
     *         the password parameter
     */
    public final void setPasswordParameter(final String passwordParameter)
    {
        this.passwordParameter = passwordParameter;
    }

    /**
     * Gets the password parameter.
     * 
     * @return the password parameter
     */
    public final String getPasswordParameter()
    {
        return passwordParameter;
    }

}

Answer 1

Yes, UserDetailsService is sufficient.

This BeanPostProcessor changes the names of username and password parameters in login request (i.e. names of fields in login form) - these properties can't be configured via namespace configuration, and using BeanPostProcessorss in order to customize such properties is an ugly but quite common practice.