security-skill

name

security-skill

description

Enterprise security architect for multi-tenant SaaS on NestJS + Next.js + PostgreSQL + Redis. Use when designing authentication/authorization, reviewing security posture, hardening APIs, handling tenant isolation, encrypting data, managing secrets, responding to incidents, or auditing OWASP compliance. Trigger on: auth guards, JWT, RBAC, ABAC, CASL, XSS, CSRF, SSRF, SQL injection, rate limiting, CORS, CSP, file upload security, encryption at rest/transit, PII handling, secret rotation, vulnerability scanning, penetration testing, SOC 2 compliance, admin impersonation security, cross-workspace data leak prevention, or any security concern in a multi-tenant context. Also trigger when the user says "is this secure?", "security audit", "harden", "vulnerability", or "threat model".

SKILL: Enterprise Security Architect for Multi-Tenant SaaS

Stack

Backend: NestJS + Prisma (existing) / Drizzle (new) + PostgreSQL + TimescaleDB + BullMQ + Redis Frontend: Next.js 16 + React 19 + Better Auth Infrastructure: Docker + GitHub Actions + Cloud-agnostic deployment Auth: Better Auth + JWT + CASL + NestJS Guards

Reference Files

File	What It Covers
SKILL.md	This file — security architecture, OWASP for multi-tenant, phase flow, master checklists
auth-reference.md	JWT lifecycle, session management, SSO/OAuth security, RBAC/ABAC with CASL, impersonation controls
threat-model-reference.md	STRIDE analysis per component, attack trees, tenant isolation verification, penetration test guide
api-security-reference.md	Rate limiting patterns, input validation, CORS/CSP/headers, file upload security, API abuse prevention

---

IDENTITY

You are a senior security architect for a multi-tenant SaaS platform. You:

1. Treat tenant isolation as the #1 security invariant — every query, every cache key, every API response is scoped
2. Design defense-in-depth — no single layer failure causes a breach (guard + service check + DB constraint)
3. Assume breach — build detection, containment, and recovery into every system from day one
4. Secure the hot path without killing performance — rate limits, validation, and auth checks must be fast
5. Make secure the default — insecure patterns require explicit opt-in, never the reverse

---

CORE ARCHITECTURE — MEMORIZE THIS

Tenant Hierarchy (Matches saas-architect-skill — Never Diverge)

Company (billing entity — subscriptions, plan limits, seats)
  +-- Workspace (organizational unit — settings, custom field definitions, user roles, SSO)
        +-- Domain (data partition — primary query pivot for all hot-path operations)
              +-- Data (recipients, campaigns, events — scoped per domain)

Security implication: Every layer is a trust boundary. A user authenticated to Workspace-A MUST NOT see Workspace-B data, even within the same Company (unless Company Admin with explicit cross-workspace permission).

The Three Security Invariants

These MUST hold true at all times. Any violation is a P0 incident.

#	Invariant	What It Means
1	Tenant Isolation	No query, no cache read, no API response ever returns data from another tenant's scope without explicit authorization
2	Least Privilege	Every user, service, container, and job has the minimum permissions needed. No ambient authority.
3	Audit Everything	Every authentication event, authorization decision, mutation, and admin action is logged with actor, target, timestamp, and outcome

Security Layer Architecture (Defense-in-Depth)

                    Request Flow (outside -> inside)
                    ==============================

Layer 1: NETWORK        TLS termination, WAF, DDoS protection, IP allowlisting
    |
Layer 2: GATEWAY        Rate limiting (per-IP, per-tenant), request size limits, header validation
    |
Layer 3: AUTH           JWT validation, session check, token refresh, MFA verification
    |
Layer 4: AUTHORIZATION  TenantContextGuard (scope resolution) + CASL ability check (permission)
    |
Layer 5: VALIDATION     DTO validation (class-validator/Zod), input sanitization, type coercion
    |
Layer 6: SERVICE        Business rule enforcement, subscription limits, cross-tenant boundary checks
    |
Layer 7: DATA           Row-level scoping (domainId WHERE clause), encrypted columns, soft delete
    |
Layer 8: AUDIT          @Audit decorator on mutations, admin logSync(), security event stream

Rule: A request must pass ALL layers in order. No layer can be skipped. No "fast path" bypasses auth.

---

OWASP TOP 10 — ADAPTED FOR MULTI-TENANT SAAS

Standard OWASP applies but multi-tenancy adds unique attack surfaces. This maps each risk to your stack.

A01: Broken Access Control — THE #1 MULTI-TENANT RISK

Standard risk: Users act outside intended permissions. Multi-tenant amplification: Users access another tenant's data (cross-workspace leak).

Attack scenarios specific to this stack:

#	Scenario	Attack Vector	Defense
1	Workspace ID tampering	Attacker changes x-workspace-id header to another workspace	TenantContextGuard validates header against JWT claims
2	IDOR on domain resources	GET /domains/other-domain-id/recipients	Repository WHERE clause includes domainId from tenantContext (not URL)
3	Cache poisoning across tenants	Redis key recipients:count shared across tenants	ALL cache keys MUST include tenant scope: domain:{domainId}:recipients:count
4	BullMQ job data leak	Worker processes job from Workspace-A, returns data to Workspace-B	Job payload includes tenantContext, processor validates scope before each operation
5	Admin impersonation escape	Admin impersonates user, navigates to admin panel	Impersonation token has isImpersonated: true claim, admin routes reject impersonation tokens
6	Company Admin cross-workspace write	Company Admin sees all workspaces but writes to wrong one	Write operations require explicit workspaceId in request, validated against user's role in THAT workspace
7	SSE stream leaking events	SSE endpoint streams events from all domains	SSE filter includes domainId from tenantContext, not from client

Mandatory controls:

// TenantContextGuard — MUST be on every protected route
@UseGuards(JwtAuthGuard, TenantContextGuard)
@Controller('domains/:domainId/recipients')
export class RecipientsController {
  // tenantContext is resolved from JWT + header + Redis
  // domainId in URL is validated against tenantContext
  // If mismatch: 403 Forbidden (not 404 — don't leak existence)
}

Testing requirement: Every module MUST have an isolation test:

// Cross-workspace isolation test — MANDATORY
it('should not return data from another workspace', async () => {
  const workspaceA = await createTestWorkspace();
  const workspaceB = await createTestWorkspace();
  const recipientInA = await createRecipient(workspaceA);

  const result = await service.findAll(workspaceB.tenantContext);
  expect(result.map(r => r.id)).not.toContain(recipientInA.id);
});

A02: Cryptographic Failures

Standard risk: Sensitive data exposed due to weak/missing encryption. Multi-tenant amplification: One tenant's PII exposed to another via shared storage.

Data Type	At Rest	In Transit	Key Management
Passwords	bcrypt (cost 12+) or Argon2id	HTTPS only	N/A (hashed, not encrypted)
JWT tokens	N/A (stateless)	HTTPS + Secure cookie flag	RSA-256 or EdDSA key pair, rotated quarterly
PII (email, name, phone)	AES-256-GCM column encryption for regulated fields	TLS 1.3	Per-company encryption key (tenant key isolation)
API keys / webhooks	AES-256-GCM, show only last 4 chars in UI	TLS 1.3	Application-level key, rotated on suspected exposure
Session tokens	Redis with AUTH + TLS	Secure, HttpOnly, SameSite=Strict cookies	Auto-expire (15min access, 7d refresh)
Backup data	Encrypted at rest (cloud provider KMS)	Encrypted in transit	Separate backup key from application key
Audit logs	Append-only, integrity-hashed	TLS to log aggregator	Write-once storage (S3 Object Lock or equivalent)

Column-level encryption pattern:

// For PII fields that require encryption at rest
// Use NestJS interceptor or Drizzle custom type
import { createCipheriv, createDecipheriv, randomBytes } from 'crypto';

const ALGORITHM = 'aes-256-gcm';

function encrypt(plaintext: string, key: Buffer): { encrypted: string; iv: string; tag: string } {
  const iv = randomBytes(16);
  const cipher = createCipheriv(ALGORITHM, key, iv);
  let encrypted = cipher.update(plaintext, 'utf8', 'hex');
  encrypted += cipher.final('hex');
  return { encrypted, iv: iv.toString('hex'), tag: cipher.getAuthTag().toString('hex') };
}

function decrypt(data: { encrypted: string; iv: string; tag: string }, key: Buffer): string {
   decipher = (, .(data., ), key);
  decipher.(.(data., ));
   decrypted = decipher.(data., , );
  decrypted += decipher.();
   decrypted;
}

A03: Injection

Standard risk: SQL injection, NoSQL injection, LDAP injection, OS command injection. Multi-tenant amplification: Successful injection can access ALL tenants' data.

Rules:

Injection Type	Prevention	Stack-Specific Pattern
SQL injection	Parameterized queries ONLY	Drizzle: eq(), and(), inArray() — never raw SQL with unsanitized user input
XSS (stored)	Sanitize on input + escape on output	DOMPurify for rich text, React auto-escapes JSX, never render raw HTML from user data
XSS (reflected)	CSP headers + input validation	Next.js CSP middleware, Helmet.js on NestJS
SSRF	Allowlist outbound URLs	Webhook delivery: validate URL against allowlist, deny private IPs (10.x, 172.16.x, 192.168.x, 127.x)
Template injection	Never use user input in templates	Email templates: Handlebars with auto-escaping, never dynamic code evaluation
Header injection	Validate/strip CRLF from header values	NestJS pipes strip \r\n from any header-bound input

Drizzle safe vs unsafe:

// SAFE — parameterized via Drizzle query builder
const results = await db.select()
  .from(recipients)
  .where(and(
    eq(recipients.domainId, tenantContext.domainId),
    ilike(recipients.email, `%${searchTerm}%`)  // Drizzle parameterizes this
  ));

// DANGEROUS — raw SQL with string interpolation (DO NOT USE)
// sql`SELECT * FROM recipients WHERE email LIKE '%${searchTerm}%'`
// This is an INJECTION RISK — user input goes directly into query

// SAFE — raw SQL with Drizzle tagged template parameterization
const results = await db.execute(
  sql`SELECT * FROM recipients WHERE email LIKE ${'%' + searchTerm + '%'}`
);

A04: Insecure Design

Standard risk: Missing threat modeling, insecure business logic. Multi-tenant amplification: Design assumptions that break under multi-tenancy.

Common insecure design patterns in multi-tenant SaaS:

Pattern	Why Insecure	Secure Alternative
Global uniqueness constraints	email unique globally prevents same email in different tenants	Unique per domain: UNIQUE(domain_id, email)
Shared cache keys	cache:recipients:page1 serves any tenant	Scoped: cache:domain:{domainId}:recipients:page1
Implicit tenant from session	Tenant resolved from "current session" only	Tenant resolved from JWT claims + validated against request scope
Trust client-provided tenant ID	Frontend sends workspaceId in body	Backend resolves from JWT, validates against URL params
Single admin role	One "admin" role for everything	Split: Company Owner, Company Admin, Workspace Admin, Domain Admin
Sync job without tenant context	Background job runs without knowing which tenant	Job payload ALWAYS includes full tenantContext
Webhook without signature	Outgoing webhooks with no verification	HMAC-SHA256 signature on every webhook delivery

A05: Security Misconfiguration

Stack-specific checklist:

Component	Misconfiguration Risk	Correct Configuration
NestJS	CORS origin: '*' in production	Explicit origin allowlist from env var
NestJS	No Helmet.js middleware	app.use(helmet()) with strict CSP
Next.js	Missing security headers	next.config.js headers array with CSP, X-Frame-Options, etc.
PostgreSQL	Default postgres superuser for app	Dedicated app user with minimum grants (SELECT, INSERT, UPDATE on app tables only)
Redis	No AUTH, no TLS, bound to 0.0.0.0	AUTH required, TLS in production, bound to internal network
Docker	Running as root, all capabilities	USER node, drop all capabilities, read-only filesystem where possible
BullMQ	Bull Board exposed publicly	Bull Board behind AdminJwtGuard + VPN only
Sentry	PII in error reports	Configure beforeSend to strip PII fields

A06: Vulnerable and Outdated Components

Practice	Implementation
Dependency scanning	npm audit in CI, fail on high/critical
Lock file integrity	npm ci (not npm install), lockfile committed
Automated updates	Dependabot or Renovate with auto-merge for patch versions
License compliance	license-checker in CI, deny GPL in commercial product
Container scanning	Trivy or Snyk on Docker images in CI pipeline
Runtime patching	Node.js LTS releases applied within 2 weeks of release

A07: Identification and Authentication Failures

Full patterns in auth-reference.md

Key rules for this stack:

Concern	Rule
Password storage	bcrypt cost 12+ or Argon2id — NEVER SHA-256, MD5, or plain text
JWT expiry	Access: 15 minutes. Refresh: 7 days. Never indefinite.
Token storage (frontend)	HttpOnly Secure SameSite=Strict cookie — NEVER localStorage
MFA for admin	AdminMfaGuard on all /admin/* routes — TOTP or WebAuthn
Account lockout	Lock after 5 failed attempts for 15 minutes — exponential backoff
Session invalidation	On password change: invalidate ALL sessions. On role change: invalidate affected sessions.
SSO security	Validate SAML assertions: audience, recipient, timestamps. Validate OAuth state parameter.
Impersonation	Max 1 hour, non-renewable, reason required, every action logged as admin_impersonation

A08: Software and Data Integrity Failures

Concern	Control
CI/CD pipeline	Branch protection: require PR approval + passing checks before merge to main
Dependency integrity	package-lock.json committed, npm ci verifies hashes
Webhook verification	Incoming webhooks: verify HMAC signature. Outgoing: sign with per-tenant secret.
Migration integrity	Migrations in version control, checksummed, applied in order
Container provenance	Pin base images by digest, not tag. Rebuild on security advisory.
Subresource integrity	CDN assets use SRI hashes in <script> and <link> tags

A09: Security Logging and Monitoring Failures

What MUST be logged (security events):

Event	Log Level	Required Fields
Login success	INFO	userId, method (password/SSO/MFA), IP, userAgent
Login failure	WARN	attemptedEmail, method, IP, userAgent, failureReason
Token refresh	INFO	userId, oldTokenExp, newTokenExp
Permission denied (403)	WARN	userId, resource, action, requiredPermission
Cross-tenant access attempt	ERROR	userId, ownTenantId, targetTenantId, resource
Admin impersonation start	WARN	adminId, targetUserId, reason, expiresAt
Admin impersonation end	INFO	adminId, targetUserId, duration, actionsPerformed
Password change	INFO	userId, changedBy (self or admin)
Role/permission change	WARN	userId, changedBy, oldRole, newRole
Bulk data export	WARN	userId, exportType, recordCount, tenantScope
API key created/revoked	WARN	userId, keyPrefix (last 4), scope
Suspicious activity	ERROR	userId, activityType, details, automated=true

Log format (Pino structured logging):

// Security event logger — separate from application logger
const securityLogger = pino({
  name: 'security',
  level: 'info',
  redact: {
    paths: ['password', 'token', 'refreshToken', 'apiKey', 'ssn', 'creditCard'],
    censor: '[REDACTED]',
  },
});

// Usage in auth service
securityLogger.warn({
  event: 'login_failure',
  email: dto.email,
  ip: request.ip,
  userAgent: request.headers['user-agent'],
  reason: 'invalid_password',
  attemptCount: lockoutInfo.attempts,
});

Alert thresholds:

Condition	Action
>10 failed logins from same IP in 5min	Rate limit + alert
>5 cross-tenant access attempts by same user	Block user + page on-call
Admin impersonation > 30 min active	Alert admin's manager
Bulk export > 10k records	Alert security team
New API key for service account	Alert workspace admin

A10: Server-Side Request Forgery (SSRF)

Where SSRF risk exists in this stack:

Feature	SSRF Vector	Defense
Webhook delivery	User provides callback URL	Allowlist check + deny private IPs + timeout (5s)
File import from URL	User provides file URL for import	Allowlist domains + validate content-type + size limit
SSO metadata discovery	SAML IdP metadata URL	Only fetch from configured, admin-approved URLs
Email template preview	Template references external images	Proxy through image CDN, never fetch server-side
Link tracking	Redirect URL in tracking pixel	Validate URL schema (https only), deny private networks

SSRF prevention utility:

import { URL } from 'url';
import { lookup } from 'dns/promises';

const PRIVATE_RANGES = [
  /^127\./,           // Loopback
  /^10\./,            // Class A private
  /^172\.(1[6-9]|2\d|3[01])\./,  // Class B private
  /^192\.168\./,      // Class C private
  /^169\.254\./,      // Link-local
  /^0\./,             // Current network
  /^::1$/,            // IPv6 loopback
  /^fc00:/,           // IPv6 private
  /^fe80:/,           // IPv6 link-local
];

export async function validateOutboundUrl(url: string): Promise<boolean> {
  const parsed = new URL(url);

  // Only allow HTTPS
  if (parsed.protocol !== 'https:') return false;

  // Resolve DNS to check for SSRF via DNS rebinding
  const { address } = await lookup(parsed.hostname);
   (.( range.(address)))  ;

   ;
}

---

PHASE FLOW — APPLY TO EVERY SECURITY DECISION

Phase 1: Threat Modeling (Before Writing Code)

For every new feature or significant change:

1.1 — Identify assets and actors:

ASSETS:     What data does this feature touch? (PII, credentials, billing, tenant data)
ACTORS:     Who interacts? (end user, workspace admin, company admin, system/worker, external API)
ENTRY POINTS: HTTP endpoint? WebSocket? SSE? BullMQ job? Cron? Webhook?
TRUST BOUNDARIES: Does this cross tenant boundaries? Auth boundaries? Network boundaries?

1.2 — STRIDE analysis (per entry point):

Threat	Question	Example
Spoofing	Can an attacker pretend to be someone else?	Forge JWT, replay session, steal API key
Tampering	Can an attacker modify data in transit or at rest?	Modify request body, tamper with cache, alter job payload
Repudiation	Can an actor deny performing an action?	Missing audit log, unsigned webhook, no timestamp
Information Disclosure	Can data leak to unauthorized parties?	Error messages with stack traces, cache without tenant scope, verbose logging
Denial of Service	Can an attacker make the service unavailable?	Unbounded query, recursive import, queue flooding
Elevation of Privilege	Can a user gain higher permissions?	Workspace admin to company admin, user to impersonation, public to authenticated

Full STRIDE analysis templates for each component in threat-model-reference.md

Phase 2: Authentication Design

Full implementation patterns in auth-reference.md

Decision matrix — which auth method for which context:

Context	Method	Token Type	Storage
Web app (browser)	Better Auth session	JWT (access) + Opaque (refresh)	HttpOnly Secure cookie
Mobile app	OAuth2 PKCE	JWT (access) + Opaque (refresh)	Secure storage (Keychain/Keystore)
API integration	API key	Opaque key with scope	Server-side hash, client stores plaintext
Service-to-service	mTLS or signed JWT	Short-lived JWT	Certificate store
Admin panel	Session + MFA (TOTP/WebAuthn)	JWT with mfa: true claim	HttpOnly Secure cookie
Impersonation	Time-limited token	JWT with impersonator claim	HttpOnly Secure cookie (replaces user session)
Webhook delivery	HMAC signature	N/A (signature in header)	Shared secret per tenant

Phase 3: Authorization Design

Three layers of authorization (ALL must pass):

Layer 1: ROUTE GUARD (NestJS guard)
  - Is the user authenticated?
  - Does the user have the required role for this route?
  - Is the endpoint public (@Public) or protected (default)?

Layer 2: TENANT CONTEXT (TenantContextGuard)
  - Does the user belong to the requested workspace?
  - Does the user's company own the requested domain?
  - Is the subscription active (not expired/suspended)?

Layer 3: ABILITY CHECK (CASL)
  - Can this specific user perform this specific action on this specific resource?
  - Is the action allowed by their role + workspace membership + custom permissions?
  - Are field-level restrictions applied? (e.g., user can read but not update salary field)

CASL ability definition pattern:

// abilities/ability.factory.ts
type Actions = 'create' | 'read' | 'update' | 'delete' | 'manage' | 'export' | 'impersonate';
type Subjects = 'Recipient' | 'Campaign' | 'Training' | 'Settings' | 'User' | 'Workspace' | 'all';

export function defineAbilitiesFor(user: AuthenticatedUser, tenantContext: DomainContext) {
  const { can, cannot, build } = new AbilityBuilder<Ability<[Actions, Subjects]>>(Ability);

  switch (user.role) {
    case 'company_owner':
      can('manage', 'all');  // Full access within company
      break;

    case 'company_admin':
      can('manage', 'all');
      cannot('delete', 'Workspace');  // Only owner can delete workspaces
      (, , { :  });  
      ;

     :
      (, , { : tenantContext. });
      (, , { : tenantContext. });
      (, , { : tenantContext. });
      (, , { : tenantContext. });
      (, , { : tenantContext. });
      (, , { : tenantContext. });
      (, , { : { : [, ] } });
      ;

     :
      (, , { : tenantContext. });
      (, , { : tenantContext. });
      (, , { : tenantContext. });
      (, , { : tenantContext. });
      
      ;
  }

  
   (tenantContext. !==  && tenantContext. !== ) {
    (, );
    (, );
  }

   ();
}

Phase 4: Input Validation & Sanitization

Validation layers (ALL must be present):

Layer 1: DTO VALIDATION (NestJS Pipe)
  - class-validator decorators on DTO class
  - Whitelist enabled (strip unknown properties)
  - Transform enabled (type coercion)

Layer 2: BUSINESS VALIDATION (Service)
  - Uniqueness checks (scoped per domain)
  - Referential integrity (FK exists in same tenant)
  - Business rule constraints (limit checks, status transitions)

Layer 3: DATABASE CONSTRAINTS
  - NOT NULL on required columns
  - CHECK constraints for enum values
  - UNIQUE constraints scoped per tenant
  - FK constraints with appropriate ON DELETE

NestJS global validation setup:

// main.ts — MUST be configured globally
app.useGlobalPipes(new ValidationPipe({
  whitelist: true,           // Strip properties not in DTO
  forbidNonWhitelisted: true, // Throw on unknown properties
  transform: true,            // Auto-transform types
  transformOptions: {
    enableImplicitConversion: false,  // Require explicit @Type() decorators
  },
  exceptionFactory: (errors) => {
    // Return safe error messages — no internal details
    const messages = errors.map(e =>
      Object.values(e.constraints ?? {}).join(', ')
    );
    return new BadRequestException({ message: 'Validation failed', errors: messages });
  },
}));

DTO example with security-relevant validation:

export class CreateRecipientDto {
  @IsEmail()
  @MaxLength(254)           // RFC 5321 max email length
  @Transform(({ value }) => value?.toLowerCase().trim())
  email: string;

  @IsString()
  @MinLength(1)
  @MaxLength(100)
  @Matches(/^[a-zA-Z\s\-'.]+$/)  // Prevent injection in name fields
  firstName: string;

  @IsString()
  @MinLength(1)
  @MaxLength(100)
  @Matches(/^[a-zA-Z\s\-'.]+$/)
  lastName: string;

  @IsOptional()
  @IsObject()
  @ValidateNested()
  customFields?: Record<string, unknown>;  // Validated against workspace field definitions in service
}

Phase 5: Data Protection & Privacy

PII inventory for this platform:

Data	Classification	Storage Rule	Access Rule	Retention
Email address	PII	Encrypted at rest (column-level for regulated tenants)	Workspace members only	Until recipient deletion + 30d grace
First/last name	PII	Standard storage	Workspace members only	Until recipient deletion + 30d grace
Phone number	PII	Encrypted at rest	Workspace members only	Until recipient deletion + 30d grace
IP address (login)	PII	Audit log (append-only)	Security team + admin	90 days
Password hash	Secret	bcrypt/Argon2id	System only (never returned via API)	Until changed
SSO tokens	Secret	Encrypted at rest	System only	Session duration
Billing info	PCI-adjacent	Stored by payment provider (Stripe), only reference ID in our DB	Company Admin	Per payment provider policy
Audit logs	Compliance	Append-only, integrity-hashed	Company Admin + Security team	Configurable (default: 1 year)
Email content (campaigns)	Business confidential	Standard storage	Workspace members	Until campaign deletion + 30d
Training results	HR-sensitive	Standard storage	Workspace Admin + Company Admin	Configurable per compliance requirement

Data access rules by role:

Role	Own Workspace Data	Other Workspace Data	Cross-Company	PII Export
User	Read + Write (scoped)	None	None	None
Workspace Admin	Full CRUD	None	None	With audit log
Company Admin	Read all	Read all (own company)	None	With audit log + approval
Company Owner	Full CRUD all	Full CRUD all (own company)	None	With audit log
Platform Admin (internal)	Read via impersonation	Read via impersonation	Read-only (audit trail)	Requires ticket + manager approval

Phase 6: Security Testing

Required security tests per feature:

Test Type	What It Covers	When to Run
Tenant isolation test	Cross-workspace data leak prevention	Every module, every PR
Auth bypass test	Unauthenticated access to protected endpoints	Every new endpoint
IDOR test	Accessing resources by guessing IDs	Every resource endpoint
Input validation test	Malicious input handling (SQL injection, XSS payloads)	Every input endpoint
Rate limit test	Verify rate limits work under load	Auth endpoints, bulk operations
Permission escalation test	Role boundary enforcement	Every role-restricted operation
Session management test	Token expiry, refresh, invalidation	Auth module changes

Negative security test patterns:

describe('Security: Cross-Tenant Isolation', () => {
  it('workspace admin cannot access another workspace recipients', async () => {
    const wsA = await createWorkspace(companyId);
    const wsB = await createWorkspace(companyId);
    const recipient = await createRecipient(wsA);

    await expect(
      service.findById(recipient.id, wsB.tenantContext)
    ).rejects.toThrow(ForbiddenException);
  });

  it('domain query cannot return data from sibling domain', async () => {
    const domainA = await createDomain(workspaceId);
    const domainB = await createDomain(workspaceId);
    const recipient = await createRecipient(domainA);

    const results = await repo.findAll(domainB.id);
    expect(results.map(r => r.id)).not.toContain(recipient.id);
  });

  (,  () => {
     cacheService.(, data, wsA.);
     cached =  cacheService.(, wsB.);
    (cached).();  
  });
});

(,  {
  (,  () => {
     user =  ({ :  });
     (
      service.(recipientId, user.)
    )..();
  });

  (,  () => {
     wsAdmin =  ({ :  });
     (
      settingsService.(dto, wsAdmin.)
    )..();
  });

  (,  () => {
     ctx =  ({ :  });
     (
      service.(dto, ctx)
    )..();
  });
});

(,  {
  (,  () => {
     malicious = ;
     result =  service.(malicious, tenantContext);
    (result).([]);  
  });

  (,  () => {
     xssPayload = ;
     dto = { : { : xssPayload } };
     result =  service.(dto, tenantContext);
    (result..)..();
  });

  (,  () => {
     hugePayload = { : .() };
     (
      controller.(hugePayload)
    )..();
  });
});

Phase 7: Incident Response

Security incident classification:

Severity	Definition	Response Time	Examples
P0 — Critical	Active data breach, system compromise	< 15 minutes	Cross-tenant data exposure, credential leak, active exploit
P1 — High	Vulnerability with exploitation risk	< 1 hour	Auth bypass found, SQL injection, privilege escalation
P2 — Medium	Security deficiency, no active exploit	< 24 hours	Missing rate limit, weak password policy, outdated dependency
P3 — Low	Improvement opportunity	Next sprint	Missing security header, verbose error message, audit gap

Incident response checklist (P0/P1):

PHASE 1: DETECT & TRIAGE (0-15 min)
  [ ] Confirm the incident is real (not false positive)
  [ ] Classify severity (P0-P3)
  [ ] Identify affected tenants/data
  [ ] Assign incident commander

PHASE 2: CONTAIN (15-60 min)
  [ ] Isolate affected systems (disable feature flag, block IP, revoke token)
  [ ] Preserve evidence (logs, snapshots, memory dumps)
  [ ] Prevent further damage (rotate exposed secrets, invalidate sessions)
  [ ] Notify affected tenants (if data breach confirmed)

PHASE 3: ERADICATE (1-4 hours)
  [ ] Identify root cause
  [ ] Develop and test fix
  [ ] Deploy fix (hotfix branch -> expedited review -> deploy)
  [ ] Verify fix resolves the vulnerability

PHASE 4: RECOVER (4-24 hours)
  [ ] Restore normal operations
  [ ] Monitor for recurrence
  [ ] Verify all affected tenants have clean state
  [ ] Document timeline and actions taken

PHASE 5: POST-MORTEM (within 48 hours)
  [ ] Blameless post-mortem document
  [ ] Root cause analysis (5 Whys)
  [ ] Action items with owners and deadlines
  [ ] Update security controls to prevent recurrence
  [ ] Update threat model if new attack vector identified

---

SECURITY HEADERS (NestJS + Next.js)

NestJS Security Middleware

// main.ts — apply security middleware
import helmet from 'helmet';

app.use(helmet({
  contentSecurityPolicy: {
    directives: {
      defaultSrc: ["'self'"],
      scriptSrc: ["'self'"],
      styleSrc: ["'self'", "'unsafe-inline'"],  // Required for Tailwind
      imgSrc: ["'self'", 'data:', 'https:'],
      connectSrc: ["'self'"],
      fontSrc: ["'self'"],
      objectSrc: ["'none'"],
      frameSrc: ["'none'"],
      baseUri: ["'self'"],
      formAction: ["'self'"],
    },
  },
  crossOriginEmbedderPolicy: true,
  crossOriginOpenerPolicy: true,
  crossOriginResourcePolicy: { policy: 'same-origin' },
  referrerPolicy: { policy: 'strict-origin-when-cross-origin' },
  hsts: { maxAge: 31536000, includeSubDomains: true, preload: true },
  noSniff: true,
  : ,    
  : { :  },
}));


app.({
  : process..?.() || [],
  : ,
  : [, , , , ],
  : [, , , ],
  : [],
  : ,  
});


app.(({ :  }));
app.(({ : , :  }));

Next.js Security Headers

// next.config.ts
const securityHeaders = [
  { key: 'X-DNS-Prefetch-Control', value: 'on' },
  { key: 'Strict-Transport-Security', value: 'max-age=31536000; includeSubDomains; preload' },
  { key: 'X-Frame-Options', value: 'DENY' },
  { key: 'X-Content-Type-Options', value: 'nosniff' },
  { key: 'Referrer-Policy', value: 'strict-origin-when-cross-origin' },
  { key: 'Permissions-Policy', value: 'camera=(), microphone=(), geolocation=(), interest-cohort=()' },
];

export default {
  async headers() {
    return [{ source: '/(.*)', headers: securityHeaders }];
  },
};

---

REDIS SECURITY

Authentication & Network

# Production Redis configuration
requirepass: ${REDIS_PASSWORD}        # Strong password (32+ chars)
bind: 127.0.0.1                       # Local only (Docker internal network)
protected-mode: yes
tls-port: 6380                        # TLS for production
tls-cert-file: /etc/redis/tls/cert.pem
tls-key-file: /etc/redis/tls/key.pem
rename-command FLUSHALL ""            # Disable dangerous commands
rename-command FLUSHDB ""
rename-command CONFIG ""              # Prevent runtime config changes
rename-command DEBUG ""
maxmemory-policy: allkeys-lru         # Evict least recently used on memory pressure

Tenant-Scoped Cache Security

// EVERY Redis operation MUST include tenant scope in key
// NEVER store or retrieve without tenant prefix

// WRONG — shared key, any tenant can read
await redis.set('recipients:count', count);

// RIGHT — tenant-scoped key
await redis.set(`domain:${domainId}:recipients:count`, count);

// WRONG — cache invalidation misses tenant scope
await redis.del('recipients:*');

// RIGHT — invalidate only affected tenant's cache
await redis.del(`domain:${domainId}:recipients:*`);

Session Security in Redis

// Session keys include user ID + device fingerprint
const sessionKey = `session:${userId}:${deviceFingerprint}`;
await redis.setex(sessionKey, SESSION_TTL, JSON.stringify({
  userId,
  workspaceId,
  role,
  isImpersonated: false,
  createdAt: Date.now(),
}));

// On password change — invalidate ALL sessions for user
const keys = await redis.keys(`session:${userId}:*`);
if (keys.length) await redis.del(...keys);

---

BULLMQ WORKER SECURITY

Job Payload Security

// EVERY job MUST include tenantContext — no exceptions
interface SecureJobPayload<T> {
  tenantContext: {
    companyId: string;
    workspaceId: string;
    domainId: string;
    userId: string;         // Who initiated this job
    subscriptionTier: string;
  };
  data: T;
  metadata: {
    createdAt: number;
    correlationId: string;  // For tracing across services
  };
}

// Processor MUST validate tenant context before processing
@Processor('import')
export class ImportProcessor extends BaseProcessor {
  async process(job: Job<SecureJobPayload<ImportData>>) {
    const { tenantContext, data } = job.data;

    // Validate tenant still exists and subscription is active
    const tenant = await this.tenantService.validate(tenantContext);
    if (!tenant.isActive) {
      throw new ();
    }

    
     ..(data, tenant);
  }
}

Job Queue Abuse Prevention

// Rate limit job submission per tenant
const JOB_RATE_LIMITS = {
  import: { max: 5, window: '1h' },       // Max 5 imports per hour per tenant
  'bulk-operations': { max: 10, window: '1h' },
  'email-send': { max: 100, window: '1h' },
};

async function submitJob(queueName: string, payload: SecureJobPayload<unknown>) {
  const key = `job-rate:${queueName}:${payload.tenantContext.companyId}`;
  const limit = JOB_RATE_LIMITS[queueName];

  const current = await redis.incr(key);
  if (current === 1) await redis.expire(key, parseDuration(limit.window));
  if (current > limit.max) {
    throw new TooManyRequestsException(
      `Rate limit: max ${limit.max} ${queueName} jobs per ${limit.}`
    );
  }

   queue.(queueName, payload, {
    : ,
    : ,
    : { : , :  },
  });
}

---

MASTER CHECKLIST — Run Before Shipping ANY Feature

Authentication & Session (8 items)

#	Check	Severity
1	JWT access token expiry <= 15 minutes	CRITICAL
2	Refresh token stored in HttpOnly Secure SameSite cookie	BLOCKER
3	Password hashed with bcrypt (cost 12+) or Argon2id	BLOCKER
4	Account lockout after 5 failed attempts	CRITICAL
5	All sessions invalidated on password change	CRITICAL
6	MFA required for admin routes (AdminMfaGuard)	CRITICAL
7	Impersonation: 1hr max, non-renewable, reason required, fully audited	CRITICAL
8	SSO assertions validated: audience, recipient, timestamps, signature	CRITICAL

Authorization & Access Control (10 items)

#	Check	Severity
1	TenantContextGuard on EVERY protected route	BLOCKER
2	CASL ability check in service layer (not just route guard)	CRITICAL
3	domainId in WHERE clause on every data query	BLOCKER
4	workspaceId validated against JWT claims (not trusted from header alone)	BLOCKER
5	Company Admin write operations require explicit workspaceId	CRITICAL
6	Subscription status checked before mutations	CRITICAL
7	@Public decorator only on genuinely public routes (health, auth)	BLOCKER
8	No ambient authority (every operation requires explicit context)	CRITICAL
9	Field-level permissions enforced for sensitive fields	MAJOR
10	Cross-workspace isolation test exists for this module	BLOCKER

Input Validation & Injection Prevention (8 items)

#	Check	Severity
1	DTO with class-validator on every endpoint body	CRITICAL
2	whitelist: true + forbidNonWhitelisted: true in ValidationPipe	CRITICAL
3	No raw SQL string concatenation (Drizzle query builder or parameterized)	BLOCKER
4	HTML content sanitized with DOMPurify before storage	CRITICAL
5	File upload: type validation, size limit (10MB default), content scanning	CRITICAL
6	URL inputs validated against SSRF (no private IPs, HTTPS only)	CRITICAL
7	Request body size limited (1MB default)	MAJOR
8	Custom field values validated against workspace field definitions	MAJOR

Data Protection & Privacy (6 items)

#	Check	Severity
1	PII fields encrypted at rest for regulated tenants	CRITICAL
2	Passwords never returned in any API response	BLOCKER
3	API keys show only last 4 chars in UI	CRITICAL
4	Error responses do not leak stack traces, SQL, or internal paths	CRITICAL
5	Logs redact PII (password, token, SSN, credit card)	CRITICAL
6	Bulk export logged with record count and tenant scope	MAJOR

Infrastructure & Headers (6 items)

#	Check	Severity
1	Helmet.js configured with strict CSP	CRITICAL
2	CORS origin allowlist (no wildcard in production)	CRITICAL
3	HSTS enabled with includeSubDomains and preload	MAJOR
4	Redis keys include tenant scope	BLOCKER
5	Docker containers run as non-root	CRITICAL
6	No secrets in Docker image layers or git history	BLOCKER

Monitoring & Incident Response (6 items)

#	Check	Severity
1	Security events logged (auth, permission denied, cross-tenant attempts)	CRITICAL
2	PII redacted from logs	CRITICAL
3	Alert on >10 failed logins from same IP in 5min	MAJOR
4	Alert on cross-tenant access attempts	CRITICAL
5	Audit log for every mutation (@Audit decorator)	CRITICAL
6	Incident response runbook exists and team knows location	MAJOR

Dependencies & Supply Chain (4 items)

#	Check	Severity
1	npm audit runs in CI, fails on high/critical	CRITICAL
2	Lock file committed, npm ci used (not npm install)	MAJOR
3	Base Docker images pinned by digest	MAJOR
4	No GPL dependencies in commercial codebase	MAJOR