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Zero Trust Architecture - Audit Trail Platform (ATP)

Never trust, always verify — ATP implements zero-trust security at every layer with strong identity, mTLS service mesh, policy-driven access control, and continuous verification for tamper-evident audit trail protection.

📋 Documentation Generation Plan

This document will be generated in 8 cycles. Current progress:

Cycle Topics Estimated Lines Status
Cycle 1 Zero Trust Fundamentals & ATP Principles (1-2) ~3,000 ⏳ Not Started
Cycle 2 Identity & Access Management (3-4) ~3,500 ⏳ Not Started
Cycle 3 Network Security & mTLS Mesh (5-6) ~3,000 ⏳ Not Started
Cycle 4 Policy Enforcement Architecture (7-8) ~3,000 ⏳ Not Started
Cycle 5 Data Protection & Encryption (9-10) ~2,500 ⏳ Not Started
Cycle 6 Multi-Tenancy & Isolation (11-12) ~3,000 ⏳ Not Started
Cycle 7 Threat Model & Attack Mitigation (13-14) ~3,500 ⏳ Not Started
Cycle 8 Monitoring, Testing & Compliance (15-16) ~3,000 ⏳ Not Started

Total Estimated Lines: ~24,500

Purpose & Scope

This document defines the zero-trust security architecture for the Audit Trail Platform (ATP), establishing comprehensive security controls across all layers including identity verification, network segmentation, policy enforcement, data encryption, and continuous monitoring to ensure no implicit trust and defense-in-depth protection for tamper-evident audit trail management.

Key Zero-Trust Principles for ATP - Never Trust, Always Verify: Every request authenticated and authorized regardless of source - Assume Breach: Design with expectation that perimeter will be compromised - Least Privilege: Minimal access required; continuously evaluated and enforced - Explicit Verification: Identity, device, context verified for every access - Micro-Segmentation: Network isolation at namespace, pod, and service level - Continuous Validation: Re-evaluate access throughout session lifetime - Defense-in-Depth: Layered security controls (edge, network, application, data)

ATP Zero-Trust Implementation - Azure AD Workload Identity: Strong identity for all pods and services (no secrets in environment) - mTLS Service Mesh: Encrypted service-to-service communication with automatic certificate rotation - Policy Enforcement Points (PEP): Gateway (PEP-1) and service-level (PEP-2) access control - Azure Policy & OPA: Declarative policy-as-code with versioning and validation - Network Policies: Default-deny ingress/egress with explicit allow-lists - Private Endpoints: All Azure services accessed via private links (no public internet) - WORM Storage: Immutable blob storage for tamper-evident audit trails - Azure Key Vault: Secrets and encryption keys with RBAC and audit logging

What this document covers

  • Establish zero-trust principles with ATP-specific application and rationale
  • Define identity and access management: Azure AD, Workload Identity, OIDC/OAuth2, RBAC/ABAC
  • Specify network security: mTLS service mesh, network policies, private endpoints, micro-segmentation
  • Document policy enforcement architecture: PEP-1 (Gateway), PEP-2 (Services), PDP (Policy Engine/OPA)
  • Detail data protection: Encryption at-rest and in-transit, WORM storage, tenant-scoped keys
  • Describe multi-tenancy isolation: Tenant boundaries, cross-tenant prevention, tenant context propagation
  • Outline threat model: Attack vectors (STRIDE), ATP-specific threats, mitigation strategies
  • Specify continuous monitoring: Security telemetry, anomaly detection, SIEM integration, incident response
  • Document supply chain security: Image signing, SBOM, admission policies, vulnerability scanning
  • Detail compliance controls: SOC 2, GDPR, HIPAA mappings to zero-trust controls
  • Describe break-glass procedures: Emergency access, approval workflows, time limits, audit trails
  • Outline testing and validation: Penetration testing, red team exercises, control testing

Out of scope (referenced elsewhere)

Readers & ownership

  • Security Engineering (owners): Zero-trust design, security controls, policy definitions, penetration testing
  • Platform Engineering/DevOps: Infrastructure security, network policies, service mesh, admission controllers
  • Architects: Security architecture, trust boundaries, threat modeling, integration patterns
  • Operations/SRE: Security monitoring, incident response, break-glass procedures, security drills
  • Compliance/Audit: Control framework, compliance mappings, evidence collection, attestation
  • Backend Developers: Secure coding, authentication implementation, authorization checks

Artifacts produced

  • Zero-Trust Architecture Diagrams: Trust boundaries, control flow, enforcement points
  • Identity Framework: Azure AD configuration, Workload Identity setup, token validation
  • Network Security Topology: VNet isolation, private endpoints, network policies, service mesh
  • Policy-as-Code: OPA/Rego policies, Azure Policy definitions, admission policies
  • Threat Model: STRIDE analysis, attack trees, abuse stories, mitigation controls
  • Security Control Inventory: All controls with owners, tests, evidence sources
  • mTLS Configuration: Service mesh setup, certificate management, rotation policies
  • Encryption Architecture: Key hierarchy, encryption at-rest/in-transit, tenant-scoped keys
  • Security Monitoring: SIEM integration, security dashboards, alert rules, anomaly detection
  • Penetration Test Reports: Annual pen test results, remediation tracking
  • Compliance Mappings: SOC 2 controls, GDPR requirements, HIPAA safeguards mapped to zero-trust
  • Break-Glass Procedures: Emergency access runbooks, approval workflows, audit requirements

Acceptance (done when)

  • All zero-trust principles are documented with ATP-specific implementations
  • Identity architecture is complete with Azure AD, Workload Identity, OIDC/OAuth2 flows
  • mTLS service mesh is documented with configuration, certificate management, and validation
  • Policy enforcement is specified with PEP-1/PEP-2 architecture and OPA integration
  • Network security includes network policies, private endpoints, and micro-segmentation
  • Data protection covers encryption at-rest/in-transit, WORM storage, key management
  • Threat model documents all STRIDE vectors with ATP-specific mitigations
  • Multi-tenancy isolation ensures zero cross-tenant access with layered controls
  • Monitoring and detection includes security telemetry, SIEM, anomaly detection
  • Supply chain security covers image signing, SBOM, admission policies
  • Compliance mappings link zero-trust controls to SOC 2, GDPR, HIPAA requirements
  • Testing procedures include pen testing, red team exercises, control validation
  • Documentation complete with architecture diagrams, code examples, runbooks, and cross-references

Detailed Cycle Plan

CYCLE 1: Zero Trust Fundamentals & ATP Principles (~3,000 lines)

Topic 1: Zero Trust Security Fundamentals

What will be covered:

  • What is Zero Trust?
  • Definition: Security model that eliminates implicit trust
  • Core principle: "Never trust, always verify"
  • Shift from perimeter-based to identity-based security
  • History: From "castle-and-moat" to "zero trust"

  • NIST SP 800-207 Zero Trust Architecture standard

  • Traditional Security vs Zero Trust

Aspect Traditional (Perimeter-Based) Zero Trust
Trust Model Trust inside network perimeter No implicit trust anywhere
Network Secure perimeter, trusted internal Assume breach, verify everything
Access Control Coarse-grained (VPN, firewall) Fine-grained (identity, context)
Authentication Once at perimeter Continuous re-verification
Authorization Role-based (static) Context-aware (dynamic)
Monitoring Periodic audits Continuous real-time
Segmentation Network zones (DMZ, internal) Micro-segments (per service/workload)
Encryption VPN tunnel mTLS everywhere
  • Core Zero Trust Principles

1. Verify Explicitly - Always authenticate and authorize - Use all available data (identity, device, location, behavior) - Multi-factor authentication (MFA) - Continuous validation

2. Least Privilege Access - Just-in-time (JIT) and just-enough-access (JEA) - Risk-based adaptive policies - Minimize blast radius - Time-limited access

3. Assume Breach - Minimize blast radius with segmentation - Verify end-to-end encryption - Use analytics to detect threats - Automate threat detection and response

  • Zero Trust Architecture Components
  • Policy Engine (PDP): Makes access decisions based on policy
  • Policy Enforcement Point (PEP): Enforces access decisions
  • Policy Administrator: Establishes communication path
  • Identity Provider (IdP): Authenticates users and devices

  • Data Sources: Context for decisions (threat intelligence, device compliance)

  • Why Zero Trust for ATP?

  • Audit Platform Mission: Cannot trust any component - audit platform audits itself
  • Multi-Tenant: Absolute tenant isolation required; zero cross-tenant trust
  • Compliance: GDPR, HIPAA, SOC 2 require zero-trust controls
  • Tamper-Evidence: Zero trust prevents unauthorized modification of audit trails
  • Cloud-Native: Distributed across Azure services; no trusted perimeter
  • External Integrations: Many external systems; cannot trust producers
  • Insider Threats: Even ATP operators cannot be fully trusted

Code Examples: - Zero trust decision flow (pseudocode) - Identity verification code - Context evaluation example

Diagrams: - Traditional vs zero trust architecture - Zero trust components - ATP zero trust layers - Decision flow diagram

Deliverables: - Zero trust fundamentals guide - Principles documentation - ATP rationale for zero trust - Comparison with traditional security

Topic 2: ATP Zero-Trust Architecture Overview

What will be covered:

  • ATP's Five-Layer Zero-Trust Model

Layer 1: Network Security - VNet isolation per environment - Private endpoints for all Azure services - Default-deny network policies - mTLS service mesh (Linkerd or Istio) - Azure Front Door with WAF

Layer 2: Identity & Access - Azure AD for user authentication - Azure AD Workload Identity for pods - OIDC/OAuth2 for external integrations - RBAC and ABAC for authorization - Short-lived tokens with automatic rotation

Layer 3: Application Security - API Gateway as Policy Enforcement Point (PEP-1) - Service-level authorization (PEP-2) - Input validation and sanitization - Rate limiting and quotas - Correlation and audit logging

Layer 4: Data Security - Encryption at-rest (Azure Storage with CMK) - Encryption in-transit (TLS 1.3, mTLS) - WORM storage for immutability - Tenant-scoped encryption keys - Field-level encryption for PII

Layer 5: Operational Security - Continuous monitoring (Azure Monitor, Azure Sentinel) - Anomaly detection with AI/ML - SIEM integration for security events - Incident response automation - Security audit trails

  • ATP Trust Boundaries
flowchart TB
    subgraph "Trust Boundary 1: Edge"
        INTERNET[Public Internet]
        AFD[Azure Front Door + WAF]
        APIM[API Management]
    end

    subgraph "Trust Boundary 2: AKS Cluster (mTLS Mesh)"
        ADMISSION[Admission Controllers]
        GATEWAY[API Gateway PEP-1]
        SERVICES[ATP Services PEP-2]
        NETPOL[Network Policies]
    end

    subgraph "Trust Boundary 3: Azure PaaS (Private Link)"
        ASB[Service Bus]
        KV[Key Vault + HSM]
        BLOB[Blob Storage WORM]
        SQL[Azure SQL]
        MONITOR[Azure Monitor]
    end

    subgraph "Trust Boundary 4: Control Plane"
        AAD[Azure AD]
        POLICY[Policy Engine OPA]
        RBAC[RBAC/ABAC]
    end

    INTERNET -->|HTTPS| AFD
    AFD -->|WAF Rules| APIM
    APIM -->|JWT Validation| GATEWAY
    GATEWAY -->|mTLS| SERVICES
    SERVICES -->|Private Endpoint| ASB
    SERVICES -->|Private Endpoint| KV
    SERVICES -->|Private Endpoint| BLOB
    SERVICES -->|Private Endpoint| SQL

    AAD -->|Identity| GATEWAY
    AAD -->|Workload Identity| SERVICES
    POLICY -->|Decisions| GATEWAY
    POLICY -->|Decisions| SERVICES
Hold "Alt" / "Option" to enable pan & zoom
  • Zero-Trust Control Points
  • Edge (AFD + WAF): TLS termination, WAF rules, bot protection, DDoS
  • API Gateway (PEP-1): Authentication, tenant resolution, rate limiting, coarse-grained authZ
  • Services (PEP-2): Fine-grained ABAC, classification checks, data access control
  • Service Mesh: mTLS, identity-based routing, circuit breakers
  • Network Policies: Default-deny ingress/egress, explicit allow-lists
  • Admission Controllers: Pod security, image verification, policy validation

  • Data Layer: RLS (Row-Level Security), tenant partitioning, encryption

  • ATP Security Objectives

  • Confidentiality: Prevent unauthorized access across tenants and classifications
  • Integrity: Tamper-evident storage with cryptographic proofs
  • Availability: Resilient controls, graceful degradation, circuit breakers
  • Accountability: Complete audit trail of all access and changes
  • Non-Repudiation: Cryptographically signed operations, immutable logs

Code Examples: - Trust boundary validation code - Zero-trust decision matrix - Layer-by-layer security checks

Diagrams: - ATP five-layer zero-trust model - Trust boundaries with controls - Security control flow - Defense-in-depth layers

Deliverables: - Zero-trust architecture specification - Trust boundaries documentation - Control points catalog - Security objectives mapping

CYCLE 2: Identity & Access Management (~3,500 lines)

Topic 3: Identity Architecture

What will be covered:

  • Azure AD for User Authentication
  • OIDC/OAuth 2.0 integration
  • Multi-Factor Authentication (MFA) required
  • Conditional Access policies
  • Device compliance requirements

  • Token lifetime and refresh

  • Azure AD Workload Identity for Pods

  • Federated identity for Kubernetes workloads
  • Pod-to-Azure service authentication (no secrets!)
  • Service Account annotations
  • OIDC token exchange

  • Audience and scope validation

  • Service-to-Service Authentication

  • mTLS certificates from service mesh
  • SPIFFE/SPIRE identity (or equivalent)
  • JWT tokens with service identity

  • Mutual authentication

  • Identity Propagation

  • User identity through API Gateway → Services
  • Service identity via mTLS certificates
  • Tenant context in every request

  • Correlation ID for tracing

  • Token Management

  • Short-lived tokens (1 hour)
  • Automatic token refresh
  • Token revocation
  • JTI (JWT ID) replay protection

Complete specifications for identity management

Topic 4: Authorization and Access Control

What will be covered:

  • RBAC (Role-Based Access Control)
  • Roles: Admin, Operator, Auditor, Viewer
  • Permissions per role
  • Kubernetes RBAC for pod access

  • Azure RBAC for resource access

  • ABAC (Attribute-Based Access Control)

  • Tenant-scoped access (TenantId attribute)
  • Classification-based access (data sensitivity)
  • Region-based access (data residency)
  • Time-based access (business hours only)

  • Risk-based access (anomaly score)

  • Policy-as-Code with OPA

  • Open Policy Agent (OPA) integration
  • Rego policy language
  • Policy bundles (signed and versioned)
  • Policy decision caching

  • Policy hot-reload

  • Policy Enforcement Points (PEP)

  • PEP-1 (API Gateway): Coarse-grained, deny-by-default
  • PEP-2 (Services): Fine-grained ABAC per operation

  • Policy evaluation latency (<10ms)

  • Continuous Authorization

  • Re-evaluate access on every request
  • No long-lived sessions without re-validation
  • Context changes trigger re-authorization
  • Anomaly detection revokes access

Complete authorization specifications

CYCLE 3: Network Security & mTLS Mesh (~3,000 lines)

Topic 5: Network Segmentation and Isolation

What will be covered:

  • VNet Isolation
  • Separate VNets per environment (dev, test, staging, production)
  • VNet peering for cross-environment (controlled)
  • No public IPs on application resources

  • Network Security Groups (NSGs)

  • Private Endpoints

  • All Azure services via Private Link
  • Service Bus, Key Vault, Storage, SQL via private endpoints
  • No public internet access to data stores

  • DNS configuration for private endpoints

  • Network Policies (Kubernetes)

  • Default-deny all ingress and egress
  • Explicit allow-lists for service-to-service
  • Namespace isolation
  • Pod-to-pod communication rules

  • DNS and monitoring exceptions

  • Micro-Segmentation

  • Namespace per bounded context
  • Network policy per service
  • Limit blast radius of compromised pod
  • East-west traffic control

Complete network security specifications

Topic 6: mTLS Service Mesh

What will be covered:

  • Service Mesh Overview (Linkerd or Istio)
  • Automatic mTLS between services
  • Identity-based service authentication
  • Traffic management and routing

  • Observability (metrics, traces, logs)

  • mTLS Configuration

  • Automatic certificate issuance
  • Certificate rotation (daily)
  • Cipher suites and TLS version (TLS 1.3)

  • Mutual authentication verification

  • Service Identity

  • SPIFFE identity for each service
  • Service Account as identity
  • Certificate includes service identity

  • Identity validation on each request

  • Traffic Encryption

  • All service-to-service traffic encrypted
  • Zero plaintext internal communication
  • Certificate pinning
  • Perfect forward secrecy (PFS)

Complete service mesh specifications

CYCLE 4: Policy Enforcement Architecture (~3,000 lines)

Topic 7: Policy Enforcement Points (PEP)

What will be covered:

  • PEP-1: API Gateway
  • First line of defense
  • Authentication validation
  • Tenant resolution
  • Rate limiting enforcement
  • Coarse-grained authorization

  • Request shaping and normalization

  • PEP-2: Service-Level Enforcement

  • Fine-grained ABAC
  • Classification-based access
  • Resource-level authorization
  • Data redaction based on clearance

  • Operation-level controls

  • Policy Decision Point (PDP)

  • Open Policy Agent (OPA)
  • Policy evaluation engine
  • Policy bundles (Rego code)
  • Decision caching (<1 second)
  • Policy versioning and rollback

Complete PEP/PDP specifications

Topic 8: Policy-as-Code with OPA

What will be covered:

  • OPA Integration
  • OPA sidecar per service
  • Policy bundles from Git
  • Signed policy bundles

  • Bundle versioning

  • Rego Policy Examples

  • Tenant isolation policy
  • Classification-based access
  • Cross-region export denial

  • Rate limiting policy

  • Policy Testing

  • OPA unit tests
  • Policy simulation

  • Coverage analysis

  • Policy Observability

  • Decision logging
  • Policy version in logs
  • Deny auditing

Complete OPA implementation guide

CYCLE 5: Data Protection & Encryption (~2,500 lines)

Topic 9: Encryption Architecture

What will be covered:

  • Encryption at Rest
  • Azure Storage encryption (default)
  • Customer-Managed Keys (CMK) in Key Vault
  • Tenant-scoped encryption keys
  • Key hierarchy (KEK, DEK)

  • WORM storage for immutability

  • Encryption in Transit

  • TLS 1.3 for external connections
  • mTLS for service-to-service
  • Perfect Forward Secrecy (PFS)

  • Cipher suite selection

  • Field-Level Encryption

  • Sensitive fields encrypted separately
  • Application-level encryption
  • Key per classification level
  • Searchable encryption (if needed)

Complete encryption specifications

Topic 10: Key Management

What will be covered:

  • Azure Key Vault Integration
  • Secrets, keys, certificates storage
  • Workload Identity access (no secrets in pods)
  • Key rotation automation

  • Audit logging for all key operations

  • Key Hierarchy

  • Master Key (Azure-managed or HSM)
  • Key Encryption Keys (KEK) - per region
  • Data Encryption Keys (DEK) - per tenant

  • Envelope encryption pattern

  • Key Rotation

  • Automatic rotation schedules
  • Zero-downtime rotation
  • Key versioning
  • Rotation audit trail

Complete key management guide

CYCLE 6: Multi-Tenancy & Isolation (~3,000 lines)

Topic 11: Tenant Isolation Controls

What will be covered:

  • Tenant Context Propagation
  • X-Tenant-Id header required
  • Tenant from JWT claims
  • Validation at every layer

  • No default tenant

  • Layered Isolation

  • Network: Namespace per tenant (optional) or network policies
  • Application: Tenant validation in all services
  • Data: Tenant partition keys, RLS (Row-Level Security)
  • Cache: Tenant-scoped cache keys

  • Logs: Tenant redaction and isolation

  • Cross-Tenant Prevention

  • Deny all cross-tenant queries
  • Tenant validation before DB access
  • Audit cross-tenant attempts
  • Alert on violations

Complete tenant isolation specifications

Topic 12: Zero-Trust Multi-Tenancy

What will be covered:

  • Tenant-Scoped Resources
  • Encryption keys per tenant
  • Network policies per tenant
  • Resource quotas per tenant

  • Rate limits per tenant

  • Tenant Trust Boundaries

  • Zero trust between tenants
  • Explicit tenant context required
  • Tenant-aware logging
  • Tenant-scoped monitoring

Complete multi-tenancy zero-trust guide

CYCLE 7: Threat Model & Attack Mitigation (~3,500 lines)

Topic 13: Threat Modeling (STRIDE)

What will be covered:

  • STRIDE Analysis
  • **S**poofing: Identity theft, token replay
  • **T**ampering: Evidence modification, policy bypass
  • **R**epudiation: Deny actions, log deletion
  • **I**nformation Disclosure: Cross-tenant access, data leakage
  • **D**enial of Service: Resource exhaustion, API flooding

  • **E**levation of Privilege: Break-glass abuse, role escalation

  • ATP-Specific Threats

  • Cross-tenant leakage
  • Audit evidence tampering
  • Retention bypass
  • Residency violations
  • Break-glass misuse

  • Supply chain attacks

  • Attack Vectors and Mitigations

  • Each threat with specific mitigations
  • Defense-in-depth controls
  • Detection mechanisms
  • Response procedures

Complete threat model

Topic 14: Attack Mitigation Strategies

What will be covered:

  • Spoofing Mitigation
  • Strong authentication (Azure AD MFA)
  • Token validation (signature, expiration, audience)

  • Anti-replay (JTI tracking)

  • Tampering Mitigation

  • WORM storage (immutable)
  • Hash chains and Merkle trees
  • Digital signatures (HSM-backed)

  • Admission controllers

  • Information Disclosure Mitigation

  • Tenant isolation layers
  • Classification-based access
  • Data redaction

  • Export route validation

  • DoS Mitigation

  • Rate limiting
  • Resource quotas
  • Circuit breakers

  • Auto-scaling with limits

  • Privilege Escalation Mitigation

  • Least privilege RBAC
  • Break-glass with dual approval
  • Time-limited access (4 hours max)
  • Continuous authorization

Complete mitigation strategies

CYCLE 8: Monitoring, Testing & Compliance (~3,000 lines)

Topic 15: Security Monitoring and Detection

What will be covered:

  • Security Telemetry
  • Authentication events
  • Authorization denials
  • Policy decisions
  • Anomalous behavior

  • Key operations

  • SIEM Integration

  • Azure Sentinel
  • Log forwarding
  • Security alerts

  • Incident correlation

  • Anomaly Detection

  • Behavioral analytics
  • Threat intelligence
  • ML-based detection

  • Automated response

  • Continuous Monitoring

  • Real-time security dashboards
  • Security KPIs
  • Compliance posture

Complete monitoring specifications

Topic 16: Zero-Trust Testing and Compliance

What will be covered:

  • Security Testing
  • Penetration testing (annual)
  • Red team exercises (quarterly)
  • Control validation testing

  • Vulnerability scanning

  • Compliance Mappings

  • SOC 2 controls → Zero-trust controls
  • GDPR requirements → Zero-trust implementations

  • HIPAA safeguards → Zero-trust measures

  • Evidence Collection

  • Control execution logs
  • Policy enforcement audit trails
  • Access logs
  • Compliance reports

Complete testing and compliance guide

Summary & Implementation Plan

Implementation Phases

Phase 1: Foundations (Cycles 1-2) - 1 month - Zero-trust principles and identity architecture

Phase 2: Network & Enforcement (Cycles 3-4) - 1.5 months - Network security, mTLS mesh, policy enforcement

Phase 3: Data & Tenancy (Cycles 5-6) - 1 month - Data protection and multi-tenant isolation

Phase 4: Threats & Operations (Cycles 7-8) - 1.5 months - Threat modeling and monitoring

Success Metrics

  • Zero Cross-Tenant Access: 100% tenant isolation
  • mTLS Coverage: 100% service-to-service encrypted
  • Authentication Rate: 100% requests authenticated
  • Policy Compliance: >99.9% policy decisions cached <10ms
  • Breach Detection: MTTD (Mean Time To Detect) <5 minutes
  • Incident Response: MTTR (Mean Time To Respond) <15 minutes

Document Status: ✅ Plan Approved - Ready for Content Generation

Target Start Date: Q3 2025

Expected Completion: Q4 2025 (5 months)

Owner: Security Engineering Team

Last Updated: 2024-10-30