如何在Spring Security SecurityConfig中获取用户指定的用户名和密码？

@Configuration
@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {

    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http
            .authorizeRequests()
                .antMatchers("/login").permitAll()
                .anyRequest().authenticated()
                .and()
            .formLogin()
                .loginPage("/login")
                .defaultSuccessUrl("/dashboard")
                .and()
            .logout()
                .logoutUrl("/logout")
                .logoutSuccessUrl("/login")
                .and()
            .csrf().disable();
    }

    @Override
    protected void configure(AuthenticationManagerBuilder auth) throws Exception {
        auth
            .inMemoryAuthentication()
                .withUser("admin")
                .password("{noop}password") // 使用{noop}前缀表示密码不加密
                .roles("ADMIN");
    }
}

@PostMapping("/login")
public String login(HttpServletRequest request) {
    String username = request.getParameter("username");
    String password = request.getParameter("password");
    
    // 进行用户名和密码的验证逻辑
    
    return "redirect:/dashboard";
}