UsernamePasswordLoginFilterの拡張について

ログイン時のusernameとpassword以外に、もう一つパラメータを追加したいのですが、
その前にフィルターを拡張した際、nullが返ってきてしまいます・・・。

設定不足部分等があれば教えていただけないでしょうか。

AuthenticationFilter

java
1
2@Log4j2
3public class MyAuthenticationFilter extends UsernamePasswordAuthenticationFilter {
4	
5	@Override
6    public Authentication attemptAuthentication(HttpServletRequest request, HttpServletResponse response) {
7        
8		String username = obtainUsername(request);  
9        String password = obtainPassword(request);
10        log.info("loginfilter: "+username+" "+password);
11        
12		UsernamePasswordAuthenticationToken authRequest 
13			= new UsernamePasswordAuthenticationToken(username, password);
14		// Allow subclasses to set the "details" property
15        setDetails(request, authRequest);
16		return this.getAuthenticationManager().authenticate(authRequest);      //nullが返ってる
17	}
18	@Autowired
19	@Override
20    public void setAuthenticationManager(AuthenticationManager authenticationManager) {
21        super.setAuthenticationManager(authenticationManager);
22    }
23}
24

SecurityConfig

java
1
2@Configuration
3@EnableWebSecurity //SpringSecurity
4public class SecurityConfig extends WebSecurityConfigurerAdapter {
5
6    @Override
7    public void configure(WebSecurity web) throws Exception {
8        web.ignoring().antMatchers("/webjars/**", "/css/**");
9    }
10    
11    @Override
12    protected void configure(HttpSecurity http) throws Exception {
13        http//
14            .authorizeRequests()
15                    .antMatchers("/loginForm").permitAll()
16                    .anyRequest().authenticated()
17            .and()
18            .formLogin().loginProcessingUrl("/login")
19                    .loginPage("/loginForm")
20                    .failureUrl("/loginForm?error")
21                    .defaultSuccessUrl("/web/loginok", true)
22
23                    .usernameParameter("username").passwordParameter("password")
24                    .and()
25                    .addFilterBefore(new MyAuthenticationFilter(),MyAuthenticationFilter.class)
26            .logout()
27                    .logoutSuccessUrl("/loginForm");
28    }
29    
30    @Bean
31    PasswordEncoder passwordEncoder() {
32        return new Pbkdf2PasswordEncoder(); 
33    }
34}
35

java.lang.NullPointerException: null
	at ---.MyAuthenticationFilter.attemptAuthentication(MyAuthenticationFilter.java:38) ~[classes/:na]
	at org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:212) ~[spring-security-web-5.1.0.BUILD-SNAPSHOT.jar:5.1.0.BUILD-SNAPSHOT]
	at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) ~[spring-security-web-5.1.0.BUILD-SNAPSHOT.jar:5.1.0.BUILD-SNAPSHOT]

...

環境
java1.8
springframework2.1.0

です。
よろしくお願いいたします。