内存用户验证时，Spring boot 2.0.1引用的security 依赖是 spring security 5.X版本，此版本需要提供一个PasswordEncorder的实例，否则后台汇报错误：
java.lang.IllegalArgumentException: There is no PasswordEncoder mapped for the id "null"
并且页面毫无响应。

 package com.mmall.demo;

 import org.springframework.security.crypto.password.PasswordEncoder;

 public class MyPasswordEncoder implements PasswordEncoder {

     @Override

     public String encode(CharSequence rawPassword) {

         return rawPassword.toString();

     }

     @Override

     public boolean matches(CharSequence rawPassword, String encodedPassword) {

         return encodedPassword.equals(rawPassword);

     }

 }

 package com.mmall.demo;

 import org.springframework.context.annotation.Configuration;

 import org.springframework.security.config.annotation.authentication.builders.AuthenticationManagerBuilder;

 import org.springframework.security.config.annotation.web.builders.HttpSecurity;

 import org.springframework.security.config.annotation.web.builders.WebSecurity;

 import org.springframework.security.config.annotation.web.configuration.EnableWebSecurity;

 import org.springframework.security.config.annotation.web.configuration.WebSecurityConfigurerAdapter;

 @Configuration

 @EnableWebSecurity

 public class SpringSecurityConfig extends WebSecurityConfigurerAdapter {

     @Override

     protected void configure(AuthenticationManagerBuilder auth) throws Exception {

         auth.inMemoryAuthentication().

                 passwordEncoder(new MyPasswordEncoder()).

                 withUser("admin").password("123456").roles("ADMIN");

     }

     @Override

     protected void configure(HttpSecurity http) throws Exception {

        http.authorizeRequests()

                .antMatchers("/").permitAll()

                .anyRequest().authenticated()

                .and()

                .logout().permitAll()

                .and()

                .formLogin();

        http.csrf().disable();

     }

     @Override

     public void configure(WebSecurity web) throws Exception {

         web.ignoring().antMatchers("/js/**","/css/**","/image/**");

     }

 }