How to Integrate jCasbin for Dynamic Permission Management in Spring Boot

Preface

As a backend developer, the author finds Shiro cumbersome for distributed projects and introduces jCasbin as a lightweight alternative for permission management.

Preparation

The example uses Spring Boot 1.5.10, but any version works.

1. Maven Dependency

<dependency>
    <groupId>org.casbin</groupId>
    <artifactId>jcasbin</artifactId>
    <version>1.1.0</version>
</dependency>
<dependency>
    <groupId>org.casbin</groupId>
    <artifactId>jdbc-adapter</artifactId>
    <version>1.1.0</version>
</dependency>

2. Configuration Files

jCasbin stores roles and permissions in model.conf and policy.csv. These files can also be loaded from a database.

In application.properties configure the database and model path:

org.jcasbin.url=jdbc:mysql://localhost:3306/casbin?useSSL=false
org.jcasbin.driver-class-name=com.mysql.jdbc.Driver
org.jcasbin.username=root
org.jcasbin.password=root
org.jcasbin.model-path=conf/authz_model.conf

2. Initialize Permission Information

Create a class that implements InitializingBean to load the Enforcer at container startup.

@Component
public class EnforcerFactory implements InitializingBean {
    private static Enforcer enforcer;
    @Autowired
    private EnforcerConfigProperties enforcerConfigProperties;
    @Override
    public void afterPropertiesSet() throws Exception {
        EnforcerConfigProperties config = enforcerConfigProperties;
        JDBCAdapter jdbcAdapter = new JDBCAdapter(
            config.getDriverClassName(), config.getUrl(), config.getUsername(),
            config.getPassword(), true);
        enforcer = new Enforcer(config.getModelPath(), jdbcAdapter);
        enforcer.loadPolicy();
    }
    public static boolean addPolicy(Policy policy) {
        boolean added = enforcer.addPolicy(policy.getSub(), policy.getObj(), policy.getAct());
        enforcer.savePolicy();
        return added;
    }
    public static boolean removePolicy(Policy policy) {
        boolean removed = enforcer.removePolicy(policy.getSub(), policy.getObj(), policy.getAct());
        enforcer.savePolicy();
        return removed;
    }
    public static Enforcer getEnforcer() { return enforcer; }
}

The accompanying EnforcerConfigProperties class holds database and model configuration fields with getters and setters.

public class EnforcerConfigProperties {
    private String url;
    private String driverClassName;
    private String username;
    private String password;
    private String modelPath;
    // getters and setters omitted for brevity
    @Override
    public String toString() {
        return "EnforcerConfigProperties [url=" + url + ", driverClassName=" + driverClassName +
               ", username=" + username + ", password=" + password + ", modelPath=" + modelPath + "]";
    }
}

A simple Policy POJO encapsulates sub (subject), obj (object), and act (action).

public class Policy {
    private String sub; // user or role
    private String obj; // resource, e.g., /user/*
    private String act; // HTTP method, e.g., GET
    public Policy() {}
    public Policy(String sub, String obj, String act) {
        this.sub = sub; this.obj = obj; this.act = act;
    }
    // getters and setters omitted
    @Override
    public String toString() {
        return "Policy [sub=" + sub + ", obj=" + obj + ", act=" + act + "]";
    }
}

3. Usage

1. Permission Control

Implement a servlet filter that checks permissions with enforcer.enforce(user, path, method).

@WebFilter(urlPatterns = "/*", filterName = "JCasbinAuthzFilter")
@Order(Ordered.HIGHEST_PRECEDENCE)
public class JCasbinAuthzFilter implements Filter {
    private static final Logger log = LoggerFactory.getLogger(JCasbinAuthzFilter.class);
    private static Enforcer enforcer;
    @Override
    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) req;
        HttpServletResponse response = (HttpServletResponse) res;
        String user = request.getParameter("username");
        String path = request.getRequestURI();
        String method = request.getMethod();
        enforcer = EnforcerFactory.getEnforcer();
        if (path.contains("anon")) {
            chain.doFilter(request, response);
        } else if (enforcer.enforce(user, path, method)) {
            chain.doFilter(request, response);
        } else {
            log.info("Access denied");
            Map<String, Object> result = new HashMap<>();
            result.put("code", 1001);
            result.put("msg", "User lacks permission");
            result.put("data", null);
            response.setCharacterEncoding("UTF-8");
            response.setContentType("application/json");
            response.getWriter().write(JSONObject.toJSONString(result, SerializerFeature.WriteMapNullValue));
        }
    }
    // init and destroy omitted
}

2. Add / Delete Permissions

Expose REST endpoints that call the factory methods to modify policies at runtime without restarting the server.

@PutMapping("/anon/role/per")
public ResultBO<Object> addPer() {
    EnforcerFactory.addPolicy(new Policy("alice", "/user/list", "*"));
    return ResultTool.success();
}

@DeleteMapping("/anon/role/per")
public ResultBO<Object> deletePer() {
    EnforcerFactory.removePolicy(new Policy("alice", "/user/list", "*"));
    return ResultTool.success();
}

Conclusion

The author notes that jCasbin can also be combined with Spring Cloud Zuul by creating a custom ZuulFilter, achieving unified login and permission control across microservices.