Java 安全架構實戰：基於 JAAS 實現自定義登入認證與資源授權完整教學

前言

Java 安全模型經歷三代演進：沙箱 (JDK 1.0) → 簽名程式碼分級信任 (JDK 1.1) → **可配置安全策略 + JAAS 雙層授權 (Java 2)**。本文完整實作一個基於 JAAS 的登入認證與檔案存取授權範例，涵蓋 Principal、LoginModule、CallbackHandler、Policy 配置全鏈路。

核心 API 速覽

完整實作程式碼

1. Principal 實作

package com.jungleford.auth;
import java.security.Principal;

public class MyPrincipal implements Principal {
    private final String name;
    public MyPrincipal(String name) { this.name = name; }
    public String getName() { return name; }
    public boolean equals(Object o) { return o instanceof MyPrincipal && name.equals(((MyPrincipal)o).getName()); }
    public String toString() { return "MyPrincipal:" + name; }
    public int hashCode() { return name.hashCode(); }
}

2. LoginModule 實作 (兩階段提交)

package com.jungleford.auth;
import javax.security.auth.*;
import javax.security.auth.callback.*;
import javax.security.auth.login.*;
import javax.security.auth.spi.*;
import java.util.*;
import java.io.IOException;

public class MyLoginModule implements LoginModule {
    private Subject subject;
    private CallbackHandler cbHandler;
    private Map sharedState, options;
    private boolean loginSucceeded = false, commitSucceeded = false;
    private String username;
    private char[] password;
    private Principal principal;

    public void initialize(Subject subject, CallbackHandler cbHandler,
                           Map sharedState, Map options) {
        this.subject = subject; this.cbHandler = cbHandler;
        this.sharedState = sharedState; this.options = options;
        System.out.println("Login module initializing...");
    }

    public boolean login() throws LoginException {
        if (cbHandler == null) throw new LoginException("No CallbackHandler");
        Callback[] cbs = { new NameCallback("Login: "), new PasswordCallback("Password: ", false) };
        try {
            cbHandler.handle(cbs);
            username = ((NameCallback)cbs[0]).getName();
            char[] tmp = ((PasswordCallback)cbs[1]).getPassword();
            password = (tmp == null) ? new char[0] : tmp.clone();
            ((PasswordCallback)cbs[1]).clearPassword();
        } catch (IOException|UnsupportedCallbackException e) {
            throw new LoginException(e.toString());
        }

        // 簡單驗證：user / letmepass
        if ("user".equals(username) && Arrays.equals(password, "letmepass".toCharArray())) {
            System.out.println("MyLoginModule: Authentication pass!");
            loginSucceeded = true;
            return true;
        } else {
            System.out.println("MyLoginModule: Authentication failed!");
            loginSucceeded = false;
            cleanup();
            throw new FailedLoginException("user".equals(username) ? "Password incorrect!" : "Username incorrect!");
        }
    }

    public boolean commit() throws LoginException {
        if (!loginSucceeded) return false;
        principal = new MyPrincipal(username);
        subject.getPrincipals().add(principal);
        System.out.println("MyLoginModule: Add a new principal to current subject.");
        cleanup();
        commitSucceeded = true;
        return true;
    }

    public boolean abort() throws LoginException {
        if (loginSucceeded && !commitSucceeded) {
            loginSucceeded = false; cleanup(); principal = null;
        } else if (commitSucceeded) {
            logout();
        }
        return true;
    }

    public boolean logout() throws LoginException {
        subject.getPrincipals().remove(principal);
        loginSucceeded = commitSucceeded = false;
        cleanup();
        principal = null;
        return true;
    }

    private void cleanup() {
        if (username != null) username = null;
        if (password != null) { Arrays.fill(password, ' '); password = null; }
    }
}

3. CallbackHandler 實作 (Swing GUI)

package com.jungleford.auth;
import javax.security.auth.callback.*;
import javax.swing.*;
import java.io.IOException;

public class MyCallbackHandler implements CallbackHandler {
    public void handle(Callback[] callbacks) throws IOException, UnsupportedCallbackException {
        String username = JOptionPane.showInputDialog(null,
            "Available name: user", "Enter your name", JOptionPane.QUESTION_MESSAGE);
        String password = JOptionPane.showInputDialog(null,
            "Available password: letmepass", "Enter your password", JOptionPane.QUESTION_MESSAGE);

        for (Callback cb : callbacks) {
            if (cb instanceof NameCallback) ((NameCallback)cb).setName(username);
            else if (cb instanceof PasswordCallback) ((PasswordCallback)cb).setPassword(password.toCharArray());
            else if (cb instanceof TextOutputCallback) {
                TextOutputCallback toc = (TextOutputCallback)cb;
                switch (toc.getMessageType()) {
                    case TextOutputCallback.INFORMATION: System.out.println(toc.getMessage()); break;
                    case TextOutputCallback.ERROR: System.err.println("Error: " + toc.getMessage()); break;
                    case TextOutputCallback.WARNING: System.err.println("Warning: " + toc.getMessage()); break;
                    default: throw new IOException("Unsupported message type");
                }
            } else throw new UnsupportedCallbackException(cb, "Unrecognized Callback");
        }
    }
}

4. PrivilegedAction 實作 (受保護資源存取)

package com.jungleford.auth;
import java.io.*;
import java.security.PrivilegedAction;

public class MyAction implements PrivilegedAction