Spring Security系列-Spring Security运行机制分析(三)

落日映苍穹つ 2022-01-30 16:29 331阅读 0赞

# 前言 #

继续第三篇，这次增加了Spring Security的DaoAuthenticationProvider和UserDetailsService类，离源代码又会更近一步。

# 从一个小程序开始 #

使用DaoAuthenticationProvider类来代替上篇中自定义类SimpleAuthenticationProvider，代码如下：

public class AuthenticationExample { 
    	public static List<AuthenticationProvider> providers = Arrays.asList(getDaoAuthentication());
        public static AuthenticationManager am = new ProviderManager(providers);
    
        public static void main(String[] args) throws Exception { 
            BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
    
            while (true) { 
                System.out.println("Please enter your username:");
                String name = in.readLine();
                System.out.println("Please enter your password:");
                String password = in.readLine();
                try { 
                    Authentication request = new UsernamePasswordAuthenticationToken(name, password);
                    Authentication result = am.authenticate(request);
                    SecurityContextHolder.getContext().setAuthentication(result);
                    break;
                } catch (AuthenticationException e) { 
                    System.out.println("Authentication failed: " + e.getMessage());
                }
            }
            System.out.println("Successfully authenticated. Security context contains: " +
                    SecurityContextHolder.getContext().getAuthentication());
        }
    
        public static AuthenticationProvider getDaoAuthentication() { 
            DaoAuthenticationProvider provider = new DaoAuthenticationProvider();
            PasswordEncoder passwordEncoder = PasswordEncoderFactories.createDelegatingPasswordEncoder();
            UserDetails admin = User.withUsername("admin")
                    .password(passwordEncoder.encode("123456"))
                    .authorities("ROLE_USER")
                    .build();
            UserDetailsService uds = new InMemoryUserDetailsManager(admin);
            provider.setPasswordEncoder(passwordEncoder);
            provider.setUserDetailsService(uds);
            return provider;
        }
    }

在getDaoAuthentication方法中，还使用了UserDetails、UserDetailsService和PasswordEncoder用来读取用户信息。这里直接用代码添加的用户，而真实项目开发会从数据库中读取用户信息。

# DaoAuthenticationProvider #

DaoAuthenticationProvider类的源代码如下，retrieveUser方法是最关键的。通过username用来获取用户相关信息。此处用到了UserDetailsServiceo类的loadUserByUsername方法，请往下看。

public class DaoAuthenticationProvider extends AbstractUserDetailsAuthenticationProvider { 
    	...
    	protected final UserDetails retrieveUser(String username,
    			UsernamePasswordAuthenticationToken authentication)
    			throws AuthenticationException { 
    		prepareTimingAttackProtection();
    		try { 
    			UserDetails loadedUser = this.getUserDetailsService().loadUserByUsername(username);
    			if (loadedUser == null) { 
    				throw new InternalAuthenticationServiceException(
    						"UserDetailsService returned null, which is an interface contract violation");
    			}
    			return loadedUser;
    		}
    		catch (UsernameNotFoundException ex) { 
    			mitigateAgainstTimingAttack(authentication);
    			throw ex;
    		}
    		catch (InternalAuthenticationServiceException ex) { 
    			throw ex;
    		}
    		catch (Exception ex) { 
    			throw new InternalAuthenticationServiceException(ex.getMessage(), ex);
    		}
    	}
    	...
    }

# UserDetailsService #

UserDetailsService接口中只定义了一个loadUserByUsername方法。实现接口的类主要有InMemoryUserDetailsManager和JdbcUserDetailsManager，一个是通过HashMap存储和读取用户信息列表，一个是通过读取数据库中的用户信息列表。

public interface UserDetailsService { 
    	UserDetails loadUserByUsername(String username) throws UsernameNotFoundException;
    }

# AbstractUserDetailsAuthenticationProvider #

回个头再来看看DaoAuthenticationProvider类的父类AbstractUserDetailsAuthenticationProvider。下面的只展示了关键代码。

public abstract class AbstractUserDetailsAuthenticationProvider implements
    		AuthenticationProvider, InitializingBean, MessageSourceAware { 
        public Authentication authenticate(Authentication authentication)
    			throws AuthenticationException { 
    		String username = (authentication.getPrincipal() == null) ? "NONE_PROVIDED"
    				: authentication.getName();
    		user = retrieveUser(username,
    				(UsernamePasswordAuthenticationToken) authentication);
    		preAuthenticationChecks.check(user);
    		additionalAuthenticationChecks(user, (UsernamePasswordAuthenticationToken) authentication);
    
    		postAuthenticationChecks.check(user);
    		Object principalToReturn = user;
    
    		if (forcePrincipalAsString) { 
    			principalToReturn = user.getUsername();
    		}
    
    		return createSuccessAuthentication(principalToReturn, authentication, user);
    	}
    	protected Authentication createSuccessAuthentication(Object principal,
    			Authentication authentication, UserDetails user) { 
    		UsernamePasswordAuthenticationToken result = new UsernamePasswordAuthenticationToken(
    				principal, authentication.getCredentials(),
    				authoritiesMapper.mapAuthorities(user.getAuthorities()));
    		result.setDetails(authentication.getDetails());
    
    		return result;
    	}
    }

可以看到，这里authenticate方法，也就是我们上篇使用到的，用于用户认证。在调用authenticate方法时，就会去调用DaoAuthenticationProvider类重写的retrieveUser方法。验证成功后，createSuccessAuthentication方法就返回了一个完整的授权后的Authentication。

# 源代码 #

github源代码：[https://github.com/camellibby/security-demo][https_github.com_camellibby_security-demo]

[https_github.com_camellibby_security-demo]: https://github.com/camellibby/security-demo