server-side-login-demo/backchannel-logout.js

const { createRemoteJWKSet, jwtVerify } = require('jose');

const BACKCHANNEL_LOGOUT_EVENT_URI =
  'http://schemas.openid.net/event/backchannel-logout';
const LOGOUT_TOKEN_REPLAY_TTL_MS = 10 * 60 * 1000;

function createBackchannelLogoutManager(options) {
  const {
    issuerUrl,
    clientId,
    jwksUrl,
    sessionStore,
    logger = console,
  } = options;

  if (!issuerUrl) {
    throw new Error('issuerUrl is required');
  }
  if (!clientId) {
    throw new Error('clientId is required');
  }
  if (!jwksUrl) {
    throw new Error('jwksUrl is required');
  }
  if (!sessionStore || typeof sessionStore.destroy !== 'function') {
    throw new Error('sessionStore.destroy is required');
  }

  const sidToSessionIds = new Map();
  const subToSessionIds = new Map();
  const sessionIdToBinding = new Map();
  const processedLogoutTokens = new Map();
  const jwks = createRemoteJWKSet(new URL(jwksUrl));

  function addSessionBinding(map, key, sessionId) {
    if (!key) {
      return;
    }

    let existing = map.get(key);
    if (!existing) {
      existing = new Set();
      map.set(key, existing);
    }
    existing.add(sessionId);
  }

  function removeSessionBindingFromMap(map, key, sessionId) {
    if (!key) {
      return;
    }

    const existing = map.get(key);
    if (!existing) {
      return;
    }

    existing.delete(sessionId);
    if (existing.size === 0) {
      map.delete(key);
    }
  }

  function removeSessionBinding(sessionId) {
    const existing = sessionIdToBinding.get(sessionId);
    if (!existing) {
      return;
    }

    removeSessionBindingFromMap(sidToSessionIds, existing.sid, sessionId);
    removeSessionBindingFromMap(subToSessionIds, existing.sub, sessionId);
    sessionIdToBinding.delete(sessionId);

    logger.log('[세션 매핑] 제거 완료', {
      sessionId,
      sid: existing.sid || '(없음)',
      sub: existing.sub || '(없음)',
    });
  }

  function registerSessionBinding(sessionId, claims) {
    const sid = typeof claims?.sid === 'string' ? claims.sid.trim() : '';
    const sub = typeof claims?.sub === 'string' ? claims.sub.trim() : '';

    removeSessionBinding(sessionId);
    sessionIdToBinding.set(sessionId, { sid, sub });
    addSessionBinding(sidToSessionIds, sid, sessionId);
    addSessionBinding(subToSessionIds, sub, sessionId);

    logger.log('[세션 매핑] 등록 완료', {
      sessionId,
      sid: sid || '(없음)',
      sub: sub || '(없음)',
      sidSessionCount: sid ? sidToSessionIds.get(sid)?.size || 0 : 0,
      subSessionCount: sub ? subToSessionIds.get(sub)?.size || 0 : 0,
    });
  }

  function getSessionIdsForLogoutClaims(claims) {
    const targets = new Set();
    const sid = typeof claims?.sid === 'string' ? claims.sid.trim() : '';
    const sub = typeof claims?.sub === 'string' ? claims.sub.trim() : '';

    if (sid && sidToSessionIds.has(sid)) {
      for (const sessionId of sidToSessionIds.get(sid)) {
        targets.add(sessionId);
      }
    }

    if (targets.size === 0 && sub && subToSessionIds.has(sub)) {
      for (const sessionId of subToSessionIds.get(sub)) {
        targets.add(sessionId);
      }
    }

    return Array.from(targets);
  }

  function destroySessionById(sessionId) {
    return new Promise((resolve, reject) => {
      sessionStore.destroy(sessionId, (err) => {
        if (err) {
          reject(err);
          return;
        }
        resolve();
      });
    });
  }

  function cleanupProcessedLogoutTokens(now = Date.now()) {
    for (const [jti, expiresAt] of processedLogoutTokens.entries()) {
      if (expiresAt <= now) {
        processedLogoutTokens.delete(jti);
      }
    }
  }

  function rememberProcessedLogoutToken(jti) {
    cleanupProcessedLogoutTokens();
    if (processedLogoutTokens.has(jti)) {
      return false;
    }
    processedLogoutTokens.set(jti, Date.now() + LOGOUT_TOKEN_REPLAY_TTL_MS);
    return true;
  }

  async function verifyLogoutToken(logoutToken) {
    const { payload, protectedHeader } = await jwtVerify(logoutToken, jwks, {
      issuer: issuerUrl,
      audience: clientId,
    });

    if (payload.nonce !== undefined) {
      throw new Error('logout_token must not include nonce');
    }

    if (!payload.events || typeof payload.events !== 'object') {
      throw new Error('logout_token is missing events claim');
    }

    if (!(BACKCHANNEL_LOGOUT_EVENT_URI in payload.events)) {
      throw new Error('logout_token is missing back-channel logout event');
    }

    const sid = typeof payload.sid === 'string' ? payload.sid.trim() : '';
    const sub = typeof payload.sub === 'string' ? payload.sub.trim() : '';
    if (!sid && !sub) {
      throw new Error('logout_token requires sid or sub');
    }

    const jti = typeof payload.jti === 'string' ? payload.jti.trim() : '';
    if (!jti) {
      throw new Error('logout_token is missing jti');
    }
    if (!rememberProcessedLogoutToken(jti)) {
      throw new Error('logout_token replay detected');
    }

    logger.log('[백채널 로그아웃] 토큰 검증 성공', {
      alg: protectedHeader.alg,
      kid: protectedHeader.kid || '(없음)',
      iss: payload.iss,
      aud: payload.aud,
      sid: sid || '(없음)',
      sub: sub || '(없음)',
      jti,
    });

    return {
      sid,
      sub,
      jti,
      payload,
    };
  }

  async function destroySessionsForLogout(claims) {
    const sessionIds = getSessionIdsForLogoutClaims(claims);
    let destroyedCount = 0;

    logger.log('[백채널 로그아웃] 세션 탐색 결과', {
      sid: claims.sid || '(없음)',
      sub: claims.sub || '(없음)',
      matchedSessionIds: sessionIds,
    });

    for (const sessionId of sessionIds) {
      removeSessionBinding(sessionId);
      try {
        await destroySessionById(sessionId);
        destroyedCount += 1;
        logger.log('[백채널 로그아웃] 세션 파기 완료', { sessionId });
      } catch (error) {
        logger.error('[백채널 로그아웃] 세션 파기 실패', {
          sessionId,
          error: error.message,
        });
      }
    }

    return { sessionIds, destroyedCount };
  }

  async function handleBackchannelLogout(req, res) {
    const logoutToken = typeof req.body.logout_token === 'string'
      ? req.body.logout_token.trim()
      : '';

    logger.log('\n[백채널 로그아웃] 요청 수신', {
      hasLogoutToken: logoutToken !== '',
      contentType: req.headers['content-type'] || '(없음)',
      userAgent: req.headers['user-agent'] || '(없음)',
    });

    if (!logoutToken) {
      logger.warn('[백채널 로그아웃] logout_token 누락');
      return res.status(400).json({ error: 'logout_token is required' });
    }

    try {
      const claims = await verifyLogoutToken(logoutToken);
      const result = await destroySessionsForLogout(claims);

      logger.log('[백채널 로그아웃] 처리 완료', {
        sid: claims.sid || '(없음)',
        sub: claims.sub || '(없음)',
        destroyedCount: result.destroyedCount,
        sessionIds: result.sessionIds,
      });

      return res.status(200).json({
        success: true,
        destroyedSessionCount: result.destroyedCount,
      });
    } catch (error) {
      logger.error('[백채널 로그아웃] 검증 또는 세션 정리 실패', error);
      return res.status(400).json({
        error: 'invalid logout token',
        detail: error.message,
      });
    }
  }

  return {
    registerSessionBinding,
    removeSessionBinding,
    handleBackchannelLogout,
  };
}

module.exports = {
  createBackchannelLogoutManager,
};