title: Using custom AccessDecisionManager with HttpSecurity addFilterBefore does not work
body: <p>The custom AccessDecisionManager does not get invoked either when filter is added or otherwise. Ideally would like to set filterBefore and custom AccessDecisionManager (using SpringBoot 1.5.2-release version). Alternately would like to call setRolePrefix on default RoleVoter. Also added DefaultRolesPrefixPostProcessor as mentioned in Section 8.3 of Spring 3 to 4 migration guide, but still RoleVoter looks for "ROLE_" prefix</p>
  
  <pre><code>@Configuration
  @EnableWebSecurity
  @EnableGlobalMethodSecurity(prePostEnabled = true, securedEnabled = true)
  public class SecurityConfig extends WebSecurityConfigurerAdapter {
      @Autowired
      AuthenticationFilter authenticationFilter;
  
      @Bean
      public AccessDecisionManager accessDecisionManager() {
          List&lt;AccessDecisionVoter&lt;? extends Object&gt;&gt; decisionVoters 
            = Arrays.asList(
              new WebExpressionVoter(),
              new RoleVoter(),
              new AuthenticatedVoter());
          return new AffirmativeBased(decisionVoters);
      }
      @Override
      protected void configure(HttpSecurity http) throws Exception {
          http
          .authorizeRequests().accessDecisionManager(accessDecisionManager())
          .anyRequest().authenticated(); 
  
          http.addFilterBefore(authenticationFilter, BasicAuthenticationFilter.class);
      }
  }
  </code></pre>