feat(auth): OTP 注册引擎（待注册态 + 验证码，review 后重做）

src/main/java/com/involutionhell/backend/usercenter/model/PendingRegistration.java

@@ -0,0 +1,16 @@
+package com.involutionhell.backend.usercenter.model;
+
+/**
+ * 待邮箱验证的注册意图（OTP 流程）。第三方登录首次、无法自动关联时创建，
+ * 存进 RegistrationService 的进程内缓存（Caffeine，短 TTL），验证码通过后才
+ * 据此建号/关联。不落库——用户放弃就随 TTL 自然消失。
+ */
+public record PendingRegistration(
+        String provider,
+        String providerUserId,
+        String displayName,
+        String avatarUrl,
+        String providerEmail,   // provider 给的邮箱（预填用），用户可在验证步改成别的
+        Long githubId
+) {
+}

src/main/java/com/involutionhell/backend/usercenter/service/RegistrationService.java

@@ -0,0 +1,180 @@
+package com.involutionhell.backend.usercenter.service;
+
+import com.github.benmanes.caffeine.cache.Cache;
+import com.github.benmanes.caffeine.cache.Caffeine;
+import com.github.benmanes.caffeine.cache.Ticker;
+import com.involutionhell.backend.common.email.ResendEmailService;
+import com.involutionhell.backend.usercenter.model.PendingRegistration;
+import java.security.SecureRandom;
+import java.time.Duration;
+import java.util.Locale;
+import java.util.Optional;
+import java.util.UUID;
+import java.util.regex.Pattern;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.stereotype.Service;
+
+/**
+ * 注册时的邮箱 OTP 引擎（ADR-001 的"规范邮箱"子系统）。职责聚焦：待注册态 +
+ * 验证码生成/发信/校验，全进程内不落库。账号建号/关联落地由调用方（wiring）在
+ * OTP 通过后做。只在"第三方登录首次、且未被已验证邮箱自动关联"时进入，不是每次登录。
+ *
+ * 安全模型（review 后重做）：
+ *   - 一个 pendingId 对应一个可变会话 RegSession，从 begin 起固定 15min 生命周期
+ *     （不被重发刷新），pending 与 OTP 同生共死，避免两缓存 TTL 错配。
+ *   - verifyAttempts 累积计在会话上、**不被重发重置**：整个会话至多 5 次校验尝试，
+ *     6 位码的爆破面恒为 5/1e6，堵住"重发归零 attempts 无限爆破"。
+ *   - 发信限流：会话内至多 5 封、两封间隔 ≥60s，防邮件轰炸。
+ *   - 校验+消费在会话锁内原子完成，双击/并发只成功一次，杜绝重复建号。
+ *   - 校验通过返回**本次实际验证通过的 email**（不是 provider 预填的未验证地址）。
+ *
+ * ponytail: 进程内 Caffeine，靠单实例 / sticky session 成立；上多实例或 GraalVM
+ * native 时会话态要迁 Redis（同 Sa-Token session、JustAuth state，见 ADR-001）。
+ * 针对特定 pendingId 的 attempts 耗尽型 DoS 由"pendingId 是随机 UUID + 15min 短命 +
+ * 控制层按 IP 限流"共同兜底，引擎层不额外处理。
+ */
+@Service
+public class RegistrationService {
+
+    private static final Logger log = LoggerFactory.getLogger(RegistrationService.class);
+    private static final SecureRandom RANDOM = new SecureRandom();
+    private static final int MAX_VERIFY_ATTEMPTS = 5;
+    private static final int MAX_SENDS = 5;
+    private static final long RESEND_COOLDOWN_NANOS = Duration.ofSeconds(60).toNanos();
+    private static final long OTP_TTL_NANOS = Duration.ofMinutes(10).toNanos();
+    private static final Duration SESSION_TTL = Duration.ofMinutes(15);
+    // 粗校验邮箱格式，挡住明显非法/注入型输入；真实有效性由"能收到码"证明。
+    private static final Pattern EMAIL_RE = Pattern.compile("^[^@\\s]+@[^@\\s]+\\.[^@\\s]+$");
+
+    /** sendOtp 结果。区分"会话过期(不可恢复,需重走注册)"与"发信失败(可重试)"等语义。 */
+    public enum SendResult { SENT, SESSION_EXPIRED, RATE_LIMITED, INVALID_EMAIL, SEND_FAILED }
+
+    /** 校验通过的注册意图 + 本次已验证的规范邮箱。 */
+    public record VerifiedRegistration(PendingRegistration pending, String verifiedEmail) {}
+
+    private final ResendEmailService emailService;
+    private final Ticker ticker;
+    private final Cache<String, RegSession> sessions;
+
+    @org.springframework.beans.factory.annotation.Autowired
+    public RegistrationService(ResendEmailService emailService) {
+        this(emailService, Ticker.systemTicker());
+    }
+
+    /** 供测试注入 FakeTicker，控制 OTP 过期与会话 TTL。 */
+    RegistrationService(ResendEmailService emailService, Ticker ticker) {
+        this.emailService = emailService;
+        this.ticker = ticker;
+        this.sessions = Caffeine.newBuilder()
+                .ticker(ticker)
+                .expireAfterWrite(SESSION_TTL)
+                .maximumSize(10_000)
+                .build();
+    }
+
+    /** 一个注册会话的可变状态。所有读改在会话锁内完成。 */
+    private static final class RegSession {
+        final PendingRegistration reg;
+        String otpEmail;
+        String otpCode;
+        long otpExpiresAtNanos;
+        int verifyAttempts;               // 累积，不被重发重置
+        int sends;
+        long lastSendAtNanos = Long.MIN_VALUE;
+
+        RegSession(PendingRegistration reg) {
+            this.reg = reg;
+        }
+    }
+
+    /** 建一个待注册会话，返回 pendingId。会话 15min 后自然过期（不被重发刷新）。 */
+    public String begin(PendingRegistration reg) {
+        String pendingId = UUID.randomUUID().toString();
+        sessions.put(pendingId, new RegSession(reg));
+        return pendingId;
+    }
+
+    /** 供 wiring 预填验证页（返回 provider 预填邮箱，非已验证）。 */
+    public Optional<PendingRegistration> getPending(String pendingId) {
+        RegSession s = sessions.getIfPresent(pendingId);
+        return s == null ? Optional.empty() : Optional.of(s.reg);
+    }
+
+    /**
+     * 给指定邮箱发 6 位验证码。限流：会话至多 {@value #MAX_SENDS} 封、间隔 ≥60s。
+     * verifyAttempts 不在此重置。
+     */
+    public SendResult sendOtp(String pendingId, String email) {
+        RegSession s = sessions.getIfPresent(pendingId);
+        if (s == null) {
+            return SendResult.SESSION_EXPIRED;
+        }
+        String normalized = email == null ? "" : email.trim();
+        if (!EMAIL_RE.matcher(normalized).matches()) {
+            return SendResult.INVALID_EMAIL;
+        }
+        String code;
+        String to;
+        synchronized (s) {
+            long now = ticker.read();
+            if (s.sends >= MAX_SENDS) {
+                return SendResult.RATE_LIMITED;
+            }
+            if (s.lastSendAtNanos != Long.MIN_VALUE && now - s.lastSendAtNanos < RESEND_COOLDOWN_NANOS) {
+                return SendResult.RATE_LIMITED;
+            }
+            code = String.format(Locale.ROOT, "%06d", RANDOM.nextInt(1_000_000));
+            s.otpEmail = normalized;
+            s.otpCode = code;
+            s.otpExpiresAtNanos = now + OTP_TTL_NANOS;
+            s.sends++;
+            s.lastSendAtNanos = now;
+            to = normalized;
+        }
+        String html = "<p>你的 InvolutionHell 注册验证码是：</p>"
+                + "<p style=\"font-size:24px;font-weight:bold;letter-spacing:4px\">" + code + "</p>"
+                + "<p>10 分钟内有效。如果不是你本人操作，忽略即可。</p>";
+        boolean sent = emailService.sendHtml(to, "InvolutionHell 注册验证码", html);
+        if (!sent) {
+            log.warn("OTP 发信失败 pendingId={}", pendingId); // 不落收件邮箱（PII）
+            return SendResult.SEND_FAILED;
+        }
+        return SendResult.SENT;
+    }
+
+    /**
+     * 校验验证码。成功则**原子**消费整个会话，返回注册意图 + 本次已验证的规范邮箱。
+     * 失败返回空（会话过期 / 未发码 / 码过期 / 超次 / 邮箱或码不符）。邮箱必须与发码
+     * 对象一致，防换邮箱绕过。attempts 累积计数，超 {@value #MAX_VERIFY_ATTEMPTS} 即锁死会话。
+     */
+    public Optional<VerifiedRegistration> verifyAndConsume(String pendingId, String email, String code) {
+        RegSession s = sessions.getIfPresent(pendingId);
+        if (s == null) {
+            return Optional.empty();
+        }
+        synchronized (s) {
+            // 会话锁内再确认未被并发消费（原子一次性）
+            if (sessions.getIfPresent(pendingId) == null) {
+                return Optional.empty();
+            }
+            if (s.otpCode == null) {
+                return Optional.empty(); // 还没 sendOtp
+            }
+            if (ticker.read() > s.otpExpiresAtNanos) {
+                return Optional.empty(); // OTP 过期
+            }
+            if (s.verifyAttempts >= MAX_VERIFY_ATTEMPTS) {
+                return Optional.empty(); // 已锁死
+            }
+            String normalized = email == null ? "" : email.trim();
+            boolean ok = s.otpEmail.equalsIgnoreCase(normalized) && s.otpCode.equals(code);
+            if (!ok) {
+                s.verifyAttempts++;
+                return Optional.empty();
+            }
+            sessions.invalidate(pendingId); // 一次性消费，锁内完成
+            return Optional.of(new VerifiedRegistration(s.reg, s.otpEmail));
+        }
+    }
+}

src/test/java/com/involutionhell/backend/usercenter/service/RegistrationServiceTests.java

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+package com.involutionhell.backend.usercenter.service;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.ArgumentMatchers.anyString;
+import static org.mockito.ArgumentMatchers.eq;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+import com.github.benmanes.caffeine.cache.Ticker;
+import com.involutionhell.backend.common.email.ResendEmailService;
+import com.involutionhell.backend.usercenter.model.PendingRegistration;
+import com.involutionhell.backend.usercenter.service.RegistrationService.SendResult;
+import com.involutionhell.backend.usercenter.service.RegistrationService.VerifiedRegistration;
+import java.time.Duration;
+import java.util.Optional;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Future;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+import org.junit.jupiter.api.Test;
+import org.mockito.ArgumentCaptor;
+
+/**
+ * OTP 引擎行为契约（review 后重做）：一次性/累积限次/重发限流/冷却/过期/邮箱绑定/
+ * 返回已验证邮箱/并发消费。用 mock 的 ResendEmailService 抓邮件正文里的码，用
+ * FakeTicker 控制时间。
+ */
+class RegistrationServiceTests {
+
+    /** 可控时钟，驱动 OTP 过期与会话 TTL / 冷却。 */
+    private static final class FakeTicker implements Ticker {
+        private long nanos = 0;
+        @Override public long read() { return nanos; }
+        void advance(Duration d) { nanos += d.toNanos(); }
+    }
+
+    private final ResendEmailService email = mock(ResendEmailService.class);
+    private final FakeTicker ticker = new FakeTicker();
+    private final RegistrationService svc = new RegistrationService(email, ticker);
+
+    private PendingRegistration reg(String providerEmail) {
+        return new PendingRegistration("discord", "snow-1", "Nick", null, providerEmail, null);
+    }
+
+    /** 发一次码并抓出邮件正文里最新的 6 位验证码（sendHtml 已 mock 成 true）。 */
+    private String sendAndCaptureCode(String pendingId, String toEmail) {
+        when(email.sendHtml(eq(toEmail), anyString(), anyString())).thenReturn(true);
+        assertThat(svc.sendOtp(pendingId, toEmail)).isEqualTo(SendResult.SENT);
+        ArgumentCaptor<String> html = ArgumentCaptor.forClass(String.class);
+        org.mockito.Mockito.verify(email, org.mockito.Mockito.atLeastOnce())
+                .sendHtml(eq(toEmail), anyString(), html.capture());
+        Matcher m = Pattern.compile("(\\d{6})").matcher(html.getAllValues().get(html.getAllValues().size() - 1));
+        assertThat(m.find()).isTrue();
+        return m.group(1);
+    }
+
+    @Test
+    void correctCodeConsumesAndReturnsVerifiedEmail() {
+        String pid = svc.begin(reg("provider-prefill@example.com"));
+        // 用户在验证步改成自己另一个邮箱
+        String code = sendAndCaptureCode(pid, "real@example.com");
+
+        Optional<VerifiedRegistration> ok = svc.verifyAndConsume(pid, "real@example.com", code);
+        assertThat(ok).isPresent();
+        assertThat(ok.get().pending().provider()).isEqualTo("discord");
+        // 关键：返回的是本次验证通过的邮箱，不是 provider 预填的未验证地址
+        assertThat(ok.get().verifiedEmail()).isEqualTo("real@example.com");
+
+        // 一次性：再验第二次失败（已消费）
+        assertThat(svc.verifyAndConsume(pid, "real@example.com", code)).isEmpty();
+    }
+
+    @Test
+    void wrongCodeFails() {
+        String pid = svc.begin(reg("a@e.com"));
+        sendAndCaptureCode(pid, "a@e.com");
+        assertThat(svc.verifyAndConsume(pid, "a@e.com", "000000")).isEmpty();
+    }
+
+    @Test
+    void emailMustMatchTheOneCodeWasSentTo() {
+        String pid = svc.begin(reg("a@e.com"));
+        String code = sendAndCaptureCode(pid, "a@e.com");
+        assertThat(svc.verifyAndConsume(pid, "attacker@e.com", code)).isEmpty();
+    }
+
+    @Test
+    void resendDoesNotResetAttempts_bruteForceCapped() {
+        String pid = svc.begin(reg("a@e.com"));
+        sendAndCaptureCode(pid, "a@e.com");
+        // 打满 5 次错码
+        for (int i = 0; i < 5; i++) {
+            assertThat(svc.verifyAndConsume(pid, "a@e.com", "111111")).isEmpty();
+        }
+        // 过冷却后重发（新码），但 attempts 不重置
+        ticker.advance(Duration.ofSeconds(61));
+        String newCode = sendAndCaptureCode(pid, "a@e.com");
+        // 即便拿到正确的新码，也因 attempts 已耗尽而失败——这就是堵住"重发无限爆破"
+        assertThat(svc.verifyAndConsume(pid, "a@e.com", newCode)).isEmpty();
+    }
+
+    @Test
+    void resendCooldownEnforced() {
+        String pid = svc.begin(reg("a@e.com"));
+        when(email.sendHtml(anyString(), anyString(), anyString())).thenReturn(true);
+        assertThat(svc.sendOtp(pid, "a@e.com")).isEqualTo(SendResult.SENT);
+        // 60s 内再发 → 限流
+        assertThat(svc.sendOtp(pid, "a@e.com")).isEqualTo(SendResult.RATE_LIMITED);
+        ticker.advance(Duration.ofSeconds(61));
+        assertThat(svc.sendOtp(pid, "a@e.com")).isEqualTo(SendResult.SENT);
+    }
+
+    @Test
+    void resendCapEnforced() {
+        String pid = svc.begin(reg("a@e.com"));
+        when(email.sendHtml(anyString(), anyString(), anyString())).thenReturn(true);
+        for (int i = 0; i < 5; i++) {
+            assertThat(svc.sendOtp(pid, "a@e.com")).isEqualTo(SendResult.SENT);
+            ticker.advance(Duration.ofSeconds(61)); // 过冷却
+        }
+        // 第 6 封超上限
+        assertThat(svc.sendOtp(pid, "a@e.com")).isEqualTo(SendResult.RATE_LIMITED);
+    }
+
+    @Test
+    void otpExpiresAfterTtl() {
+        String pid = svc.begin(reg("a@e.com"));
+        String code = sendAndCaptureCode(pid, "a@e.com");
+        ticker.advance(Duration.ofMinutes(11)); // 超 10min OTP TTL
+        assertThat(svc.verifyAndConsume(pid, "a@e.com", code)).isEmpty();
+    }
+
+    @Test
+    void invalidEmailRejected() {
+        String pid = svc.begin(reg("a@e.com"));
+        assertThat(svc.sendOtp(pid, "not-an-email")).isEqualTo(SendResult.INVALID_EMAIL);
+    }
+
+    @Test
+    void unknownPendingIsSessionExpired() {
+        assertThat(svc.sendOtp("nonexistent", "a@e.com")).isEqualTo(SendResult.SESSION_EXPIRED);
+        assertThat(svc.verifyAndConsume("nonexistent", "a@e.com", "123456")).isEmpty();
+    }
+
+    @Test
+    void verifyFailsWhenNothingSent() {
+        String pid = svc.begin(reg("a@e.com"));
+        assertThat(svc.verifyAndConsume(pid, "a@e.com", "123456")).isEmpty();
+    }
+
+    @Test
+    void concurrentConsumeSucceedsExactlyOnce() throws Exception {
+        String pid = svc.begin(reg("a@e.com"));
+        String code = sendAndCaptureCode(pid, "a@e.com");
+
+        int threads = 8;
+        ExecutorService pool = Executors.newFixedThreadPool(threads);
+        CountDownLatch start = new CountDownLatch(1);
+        AtomicInteger successes = new AtomicInteger();
+        Future<?>[] futures = new Future<?>[threads];
+        for (int i = 0; i < threads; i++) {
+            futures[i] = pool.submit(() -> {
+                try {
+                    start.await();
+                    if (svc.verifyAndConsume(pid, "a@e.com", code).isPresent()) {
+                        successes.incrementAndGet();
+                    }
+                } catch (InterruptedException ignored) {
+                    Thread.currentThread().interrupt();
+                }
+            });
+        }
+        start.countDown();
+        for (Future<?> f : futures) f.get();
+        pool.shutdown();
+
+        // 并发多线程用同一正确码，只能成功一次（原子一次性消费）
+        assertThat(successes.get()).isEqualTo(1);
+    }
+}