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1 簡介

Spring Security作為成熟且強大的安全框架，得到許多大廠的青睞，而作為前后端分離的SSO方案，JWT也在許多專案中應用，本文將介紹如何通過Spring Security實作JWT認證，

用戶與服務器互動大概如下：

客戶端獲取JWT，一般通過POST方法把用戶名/密碼傳給server；
服務端接收到客戶端的請求后，會檢驗用戶名/密碼是否正確，如果正確則生成JWT并回傳；不正確則回傳錯誤；
客戶端拿到JWT后，在有效期內都可以通過JWT來訪問資源了，一般把JWT放在請求頭；一次獲取，多次使用；
服務端校驗JWT是否合法，合法則允許客戶端正常訪問，不合法則回傳401，

2 專案整合

我們把要整合的Spring Security和JWT加入到專案的依賴中去：

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-security</artifactId>
</dependency>
<dependency>
  <groupId>io.jsonwebtoken</groupId>
  <artifactId>jjwt</artifactId>
  <version>0.9.1</version>
</dependency>

2.1 JWT整合

2.1.1 JWT工具類

JWT工具類起碼要具有以下功能：

根據用戶資訊生成JWT；
校驗JWT是否合法，如是否被篡改、是否過期等；
從JWT中決議用戶資訊，如用戶名、權限等；

具體代碼如下：

@Component
public class JwtTokenProvider {

    @Autowired JwtProperties jwtProperties;

    @Autowired
    private CustomUserDetailsService userDetailsService;

    private String secretKey;

    @PostConstruct
    protected void init() {
        secretKey = Base64.getEncoder().encodeToString(jwtProperties.getSecretKey().getBytes());
    }

    public String createToken(String username, List<String> roles) {

        Claims claims = Jwts.claims().setSubject(username);
        claims.put("roles", roles);

        Date now = new Date();
        Date validity = new Date(now.getTime() + jwtProperties.getValidityInMs());

        return Jwts.builder()//
                .setClaims(claims)//
                .setIssuedAt(now)//
                .setExpiration(validity)//
                .signWith(SignatureAlgorithm.HS256, secretKey)//
                .compact();
    }

    public Authentication getAuthentication(String token) {
        UserDetails userDetails = this.userDetailsService.loadUserByUsername(getUsername(token));
        return new UsernamePasswordAuthenticationToken(userDetails, "", userDetails.getAuthorities());
    }

    public String getUsername(String token) {
        return Jwts.parser().setSigningKey(secretKey).parseClaimsJws(token).getBody().getSubject();
    }

    public String resolveToken(HttpServletRequest req) {
        String bearerToken = req.getHeader("Authorization");
        if (bearerToken != null && bearerToken.startsWith("Bearer ")) {
            return bearerToken.substring(7);
        }
        return null;
    }

    public boolean validateToken(String token) {
        try {
            Jws<Claims> claims = Jwts.parser().setSigningKey(secretKey).parseClaimsJws(token);

            if (claims.getBody().getExpiration().before(new Date())) {
                return false;
            }

            return true;
        } catch (JwtException | IllegalArgumentException e) {
            throw new InvalidJwtAuthenticationException("Expired or invalid JWT token");
        }
    }

}

工具類還實作了另一個功能：從HTTP請求頭中獲取JWT，

2.1.2 Token處理的Filter

Filter是Security處理的關鍵，基本上都是通過Filter來攔截請求的，首先從請求頭取出JWT，然后校驗JWT是否合法，如果合法則取出Authentication保存在SecurityContextHolder里，如果不合法，則做例外處理，

public class JwtTokenAuthenticationFilter extends GenericFilterBean {

    private JwtTokenProvider jwtTokenProvider;

    public JwtTokenAuthenticationFilter(JwtTokenProvider jwtTokenProvider) {
        this.jwtTokenProvider = jwtTokenProvider;
    }

    @Override
    public void doFilter(ServletRequest req, ServletResponse res, FilterChain filterChain)
            throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) req;
        HttpServletResponse response = (HttpServletResponse) res;

        try {
            String token = jwtTokenProvider.resolveToken(request);
            if (token != null && jwtTokenProvider.validateToken(token)) {
                Authentication auth = jwtTokenProvider.getAuthentication(token);

                if (auth != null) {
                    SecurityContextHolder.getContext().setAuthentication(auth);
                }
            }
        } catch (InvalidJwtAuthenticationException e) {
            response.setStatus(HttpStatus.UNAUTHORIZED.value());
            response.getWriter().write("Invalid token");
            response.getWriter().flush();
            return;
        }

        filterChain.doFilter(req, res);
    }
}

對于例外處理，使用@ControllerAdvice是不行的，應該這個是Filter，在這里拋的例外還沒有到DispatcherServlet，無法處理，所以Filter要自己做例外處理：

catch (InvalidJwtAuthenticationException e) {
  response.setStatus(HttpStatus.UNAUTHORIZED.value());
  response.getWriter().write("Invalid token");
  response.getWriter().flush();
  return;
}

最后的return;不能省略，因為已經把要輸出的內容給Response了，沒有必要再往后傳遞，否則會報錯：

java.lang.IllegalStateException: getWriter() has already been called

2.1.3 JWT屬性

JWT需要配置一個密鑰來加密，同時還要配置JWT令牌的有效期，

@Configuration
@ConfigurationProperties(prefix = "pkslow.jwt")
public class JwtProperties {
    private String secretKey = "pkslow.key";
    private long validityInMs = 3600_000;
//getter and setter
}

2.2 Spring Security整合

Spring Security的整個框架還是比較復雜的，簡化后大概如下圖所示：

它是通過一連串的Filter來進行安全管理，細節這里先不展開講，

2.2.1 WebSecurityConfigurerAdapter配置

這個配置也可以理解為是FilterChain的配置，可以不用理解，代碼很好懂它做了什么：

@Configuration
public class SecurityConfig extends WebSecurityConfigurerAdapter {


    @Autowired
    JwtTokenProvider jwtTokenProvider;

    @Bean
    @Override
    public AuthenticationManager authenticationManagerBean() throws Exception {
        return super.authenticationManagerBean();
    }

    @Bean
    public PasswordEncoder passwordEncoder() {
        return NoOpPasswordEncoder.getInstance();
    }

    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http
            .httpBasic().disable()
            .csrf().disable()
            .sessionManagement().sessionCreationPolicy(SessionCreationPolicy.STATELESS)
            .and()
            .authorizeRequests()
            .antMatchers("/auth/login").permitAll()
            .antMatchers(HttpMethod.GET, "/admin").hasRole("ADMIN")
            .antMatchers(HttpMethod.GET, "/user").hasRole("USER")
            .anyRequest().authenticated()
            .and()
            .apply(new JwtSecurityConfigurer(jwtTokenProvider));
    }
}

這里通過HttpSecurity配置了哪些請求需要什么權限才可以訪問，

/auth/login用于登陸獲取JWT，所以都能訪問；
/admin只有ADMIN用戶才可以訪問；
/user只有USER用戶才可以訪問，

而之前實作的Filter則在下面配置使用：

public class JwtSecurityConfigurer extends SecurityConfigurerAdapter<DefaultSecurityFilterChain, HttpSecurity> {

    private JwtTokenProvider jwtTokenProvider;

    public JwtSecurityConfigurer(JwtTokenProvider jwtTokenProvider) {
        this.jwtTokenProvider = jwtTokenProvider;
    }

    @Override
    public void configure(HttpSecurity http) throws Exception {
        JwtTokenAuthenticationFilter customFilter = new JwtTokenAuthenticationFilter(jwtTokenProvider);
        http.exceptionHandling()
                .authenticationEntryPoint(new JwtAuthenticationEntryPoint())
                .and()
                .addFilterBefore(customFilter, UsernamePasswordAuthenticationFilter.class);
    }
}

2.2.2 用戶從哪來

通常在Spring Security的世界里，都是通過實作UserDetailsService來獲取UserDetails的，

@Component
public class CustomUserDetailsService implements UserDetailsService {

    private UserRepository users;

    public CustomUserDetailsService(UserRepository users) {
        this.users = users;
    }

    @Override
    public UserDetails loadUserByUsername(String username) throws UsernameNotFoundException {
        return this.users.findByUsername(username)
                .orElseThrow(() -> new UsernameNotFoundException("Username: " + username + " not found"));
    }
}

對于UserRepository，可以從資料庫中讀取，或者其它用戶管理中心，為了方便，我使用Map放了兩個用戶：

@Repository
public class UserRepository {

    private static final Map<String, User> allUsers = new HashMap<>();

    @Autowired
    private PasswordEncoder passwordEncoder;

    @PostConstruct
    protected void init() {
        allUsers.put("pkslow", new User("pkslow", passwordEncoder.encode("123456"), Collections.singletonList("ROLE_ADMIN")));
        allUsers.put("user", new User("user", passwordEncoder.encode("123456"), Collections.singletonList("ROLE_USER")));
    }

    public Optional<User> findByUsername(String username) {
        return Optional.ofNullable(allUsers.get(username));
    }
}

3 測驗

完成代碼撰寫后，我們來測驗一下：

（1）無JWT訪問，失敗

curl http://localhost:8080/admin
{"timestamp":"2021-02-06T05:45:06.385+0000","status":403,"error":"Forbidden","message":"Access Denied","path":"/admin"}

$ curl http://localhost:8080/user
{"timestamp":"2021-02-06T05:45:16.438+0000","status":403,"error":"Forbidden","message":"Access Denied","path":"/user"}

（2）admin獲取JWT，密碼錯誤則失敗，密碼正確則成功

$ curl http://localhost:8080/auth/login -X POST -d '{"username":"pkslow","password":"xxxxxx"}' -H 'Content-Type: application/json'
{"timestamp":"2021-02-06T05:47:16.254+0000","status":403,"error":"Forbidden","message":"Access Denied","path":"/auth/login"}

$ curl http://localhost:8080/auth/login -X POST -d '{"username":"pkslow","password":"123456"}' -H 'Content-Type: application/json'
eyJhbGciOiJIUzI1NiJ9.eyJzdWIiOiJwa3Nsb3ciLCJyb2xlcyI6WyJST0xFX0FETUlOIl0sImlhdCI6MTYxMjU5MDYxNCwiZXhwIjoxNjEyNTkxMjE0fQ.d4Gi50aaOsHHqpM0d8Mh1960otnZf7rlE3x6xSfakVo

（3）admin帶JWT訪問/admin，成功；訪問/user失敗

$ curl http://localhost:8080/admin -H 'Authorization: Bearer eyJhbGciOiJIUzI1NiJ9.eyJzdWIiOiJwa3Nsb3ciLCJyb2xlcyI6WyJST0xFX0FETUlOIl0sImlhdCI6MTYxMjU5MDYxNCwiZXhwIjoxNjEyNTkxMjE0fQ.d4Gi50aaOsHHqpM0d8Mh1960otnZf7rlE3x6xSfakVo'
you are admin

$ curl http://localhost:8080/user -H 'Authorization: Bearer eyJhbGciOiJIUzI1NiJ9.eyJzdWIiOiJwa3Nsb3ciLCJyb2xlcyI6WyJST0xFX0FETUlOIl0sImlhdCI6MTYxMjU5MDYxNCwiZXhwIjoxNjEyNTkxMjE0fQ.d4Gi50aaOsHHqpM0d8Mh1960otnZf7rlE3x6xSfakVo'
{"timestamp":"2021-02-06T05:51:23.099+0000","status":403,"error":"Forbidden","message":"Forbidden","path":"/user"}

（4）使用過期的JWT訪問，失敗

$ curl http://localhost:8080/admin -H 'Authorization: Bearer eyJhbGciOiJIUzI1NiJ9.eyJzdWIiOiJwa3Nsb3ciLCJyb2xlcyI6WyJST0xFX0FETUlOIl0sImlhdCI6MTYxMjU5MDQ0OSwiZXhwIjoxNjEyNTkwNTA5fQ.CSaubE4iJcYATbLmbb59aNFU1jNCwDFHUV3zIakPU64'
Invalid token

對于用戶user同樣可以測驗，這里不列出來了，

4 總結

代碼請查看：https://github.com/LarryDpk/pkslow-samples

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標籤：Java

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