CAS概念

CAS是Central Authentiction Service 的缩写，中央认证服务。CAS是Yale大学发起的开源项目，旨在为Web应用系统提供一种可靠的单点登录方法，CAS在2004年12月正式称为JA-SIG的一个项目。官网地址：https://www.apereo.org/projects/cas。

Spring Security CAS原理

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1. 用户在浏览器发起请求web系统私有资源 /private；
2. SecurityFilterChain过滤器链路到达FilterSecurityInterceptor，并抛出访问被拒绝的异常AccessDeniedException，ExceptionTranslationFilter捕获该异常并通过sendStartAuthentication方法进入CasAuthenticationEntryPoint（AuthenticationEntryPoint的实现类）；
3. CasAuthenticationEntryPoint设置重定向到CAS Server地址https://my.company.com/cas/login?service=https%3A%2F%2Fserver3.company.com%2Fwebapp%2Flogin/cas。

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1. 用户在CAS Server登录验证完后，携带ST跳转到客户端https://server3.company.com/webapp/login/cas?ticket=ST-0-ER94xMJmn6pha35CQRoZ
   ，进入CasAuthenticationFilter；
2. CasAuthenticationFilter将ST包装成UsernamePasswordAuthenticationToken请求AuthenticationManager进行认证处理；
3. AuthenticationManager将认证委托给CasAuthenticationProvider；
4. CasAuthenticationProvider使用TicketValidator向CAS Server发起ST校验请求https://server3.company.com/webapp/serviceValidate?service=https%3A%2F%2Fserver3.company.com%2Fwebapp%2Flogin/cas&ticket=ST-0-ER94xMJmn6pha35CQRoZ，成功后获取用户登录信息。
5. 最后，CasAuthenticationProvider使用AuthenticationUserDetailsService进行后置处理，一般获取更加详细的用户信息，例如权限等。

Spring Security CAS 实战

1. 引入依赖

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-security</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.security</groupId>
            <artifactId>spring-security-cas</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

2. 修改配置文件application.yml

server:
  port: 8080

base:
  url: http://localhost:8080
cas:
  server:
    url: https://cas.test.com/cas

3. 相关代码
   CasConfig.java

@Configuration
public class CasConfig {

    @Value("${cas.server.url}")
    private String casServerUrl;
    @Value("${base.url}")
    private String baseUrl;

    @Bean
    public AuthenticationEntryPoint authenticationEntryPoint() {
        CasAuthenticationEntryPoint entryPoint = new CasAuthenticationEntryPoint();
        entryPoint.setLoginUrl(casServerUrl + "/login");
        entryPoint.setServiceProperties(this.serviceProperties());
        return entryPoint;
    }

    @Bean
    protected AuthenticationManager authenticationManager() throws Exception {
        return new ProviderManager(this.casAuthenticationProvider());
    }

    @Bean
    public CasAuthenticationFilter casAuthenticationFilter(
            AuthenticationManager authenticationManager,
            ServiceProperties serviceProperties) throws Exception {
        CasAuthenticationFilter filter = new CasAuthenticationFilter();
        filter.setAuthenticationManager(authenticationManager);
        filter.setServiceProperties(serviceProperties);
        return filter;
    }

    @Bean
    public ServiceProperties serviceProperties() {
        ServiceProperties serviceProperties = new ServiceProperties();
        serviceProperties.setService(baseUrl + "/login/cas");
        serviceProperties.setSendRenew(false);
        return serviceProperties;
    }

    @Bean
    public TicketValidator ticketValidator() {
        return new Cas30ServiceTicketValidator(casServerUrl);
    }

    @Bean
    public CasAuthenticationProvider casAuthenticationProvider() {
        CasAuthenticationProvider provider = new CasAuthenticationProvider();
        provider.setServiceProperties(this.serviceProperties());
        provider.setTicketValidator(this.ticketValidator());
        provider.setAuthenticationUserDetailsService(new CustomUserDetailsService());
        provider.setKey("CAS_PROVIDER_LOCALHOST");
        return provider;
    }

    @Bean
    public SecurityContextLogoutHandler securityContextLogoutHandler() {
        return new SecurityContextLogoutHandler();
    }

    @Bean
    public LogoutFilter logoutFilter() {
        LogoutFilter logoutFilter = new LogoutFilter(casServerUrl + "/logout?service=" + baseUrl,
                securityContextLogoutHandler());
        logoutFilter.setFilterProcessesUrl("/logout/cas");
        return logoutFilter;
    }

    @Bean
    public SingleSignOutFilter singleSignOutFilter() {
        SingleSignOutFilter singleSignOutFilter = new SingleSignOutFilter();
        singleSignOutFilter.setIgnoreInitConfiguration(true);
        return singleSignOutFilter;
    }
}

CustomUserDetailsService.java

public class CustomUserDetailsService extends AbstractCasAssertionUserDetailsService {
    
    @Override
    protected UserDetails loadUserDetails(Assertion assertion) {
        // 可自定义获取用户信息
        String username = assertion.getPrincipal().getName();
        Map<String, Object> attributes = assertion.getPrincipal().getAttributes();
        return new User("admin", "admin", true, true, 
                true, true, AuthorityUtils.createAuthorityList("ROLE_ADMIN"));
    }
}

WebConfig.java

@EnableWebSecurity
public class WebConfig extends WebSecurityConfigurerAdapter {
    @Autowired
    private SingleSignOutFilter singleSignOutFilter;
    @Autowired
    private LogoutFilter logoutFilter;
    @Autowired
    private AuthenticationEntryPoint authenticationEntryPoint;
    @Autowired
    private CasAuthenticationFilter casAuthenticationFilter;

    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http.authorizeRequests()
                .antMatchers("/login/cas").permitAll()
                .anyRequest().authenticated()
                .and().httpBasic().authenticationEntryPoint(authenticationEntryPoint)
                .and()
                .addFilter(casAuthenticationFilter)
                .addFilterBefore(singleSignOutFilter, CasAuthenticationFilter.class)
                .addFilterBefore(logoutFilter, LogoutFilter.class);
    }
}

WelcomeController.java

@RequestMapping
@Controller
public class WelcomeController {

    @GetMapping("/")
    @ResponseBody
    public String index() {
        Authentication auth = SecurityContextHolder.getContext().getAuthentication();
        return "当前用户信息：" + auth.getPrincipal();
    }
}