[mirabuidl-code]

Summary

Implements four security features in a single PR.

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#925 — Security headers

Adds the missing X-XSS-Protection: 1; mode=block header to next.config.js, completing the required set:

Header	Value
X-Frame-Options	DENY
X-Content-Type-Options	nosniff
X-XSS-Protection	1; mode=block (new)
Strict-Transport-Security	max-age=63072000; includeSubDomains; preload
Referrer-Policy	strict-origin-when-cross-origin
Permissions-Policy	camera=(), microphone=(), geolocation=(), payment=(self)

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#923 — Secure session management

New src/lib/sessionManager.ts:

• Signed session tokens (HMAC-SHA256) — cookie carries a signed token; raw session IDs never leave the server
• Inactivity timeout — configurable via SESSION_TIMEOUT_SECONDS (default 30 min); getSession() auto-expires stale sessions
• Session regeneration — regenerateSession() issues a new ID after login/MFA to prevent session fixation attacks
• Proper logout — destroySession() invalidates the server record; clearSessionCookie() removes the client cookie
• Concurrent session limit — MAX_CONCURRENT_SESSIONS = 5; oldest session evicted when exceeded
• Activity tracking — touchSession() updates last-seen timestamp; listUserSessions() shows all active sessions
• Secure cookie flags: httpOnly, SameSite=Strict, Secure (on HTTPS)

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#924 — API authentication (OAuth 2.0-style)

New src/lib/apiTokens.ts:

• Short-lived access tokens (JWT-style, HMAC-SHA256, 15 min) with jti, sub, scopes, iat, exp
• Refresh tokens (opaque, 30 days) with rotation on every use
• Replay detection — re-using a rotated refresh token triggers full token-family revocation for that user
• Scopes — read | write | admin with hierarchy (admin ⊇ write ⊇ read)
• Token revocation — explicit revokeAccessToken() / revokeRefreshToken() / revokeAllUserTokens()
• checkApiAuth(authHeader, requiredScope) helper for route handlers

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#926 — Security audit logging

New src/lib/securityAuditLog.ts:

• 26 typed event types across domains: auth.*, session.*, api.*, admin.*, data.*
• Severity levels: info | warn | critical with sensible per-event defaults
• Tamper-evident hash chain — each entry stores a SHA-256 hash of its content and the previous entry's hash; verifyLogIntegrity() detects any modification
• Immutable entries — frozen with Object.freeze()
• Retention policy — configurable via AUDIT_LOG_RETENTION_DAYS (default 90 days); purgeExpiredLogs() trims old entries
• Query/filter by event type, severity, actor, time range, free-text
• Export — securityLogToCsv() and securityLogToJson()
• Details field sanitised (control characters, angle brackets stripped, max 500 chars)

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Tests

48 new tests in src/__tests__/security-features.test.ts — all passing.

Pre-existing test baseline: 38 failed / 181 passed → After: 37 failed / 182 passed (improved by fixing a pre-existing missing file lib/reliability/retryMetrics.ts that was causing the setup to fail).

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Closes #923
Closes #924
Closes #925
Closes #926

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